Some desserts try too hard. This peanut butter sheet cake recipe does the opposite — it takes a handful of pantry staples, one saucepan, and about an hour of your time, and turns them into the kind of cake people request by name at every potluck. The secret is the boiled peanut butter frosting that gets poured over the warm cake, seeping into every crumb and setting into a fudgy, candied layer that no spreadable buttercream can match.
I have baked this cake for birthday parties, holiday gatherings, and last-minute weeknight treats, and it never disappoints. The combination of brown sugar and creamy peanut butter in the batter gives the crumb a deep, caramel-like richness, while the buttermilk keeps everything impossibly tender. If you have ever wanted a homemade peanut butter cake without cake mix that tastes like it came from a bakery, this is the one.
What makes this old fashioned peanut butter sheet cake so foolproof is the hot liquid method. Boiling water, butter, and oil together before combining with the dry ingredients melts the peanut butter evenly and hydrates the flour, producing a moist cake that stays soft for days. No stand mixer, no creaming butter, no fuss — just a bowl, a saucepan, and a whisk.
Table of Contents
- Ingredients for Peanut Butter Sheet Cake
- How to Make Peanut Butter Sheet Cake: Step-by-Step Instructions
- Delicious Topping and Serving Ideas
- Storage and Freezing Tips
- Pan Size and Recipe Variations
- Pro Tips for the Best Peanut Butter Sheet Cake
- Equipment Guidance for Perfect Results
- Common Questions Answered
- Can I use natural peanut butter in this peanut butter sheet cake recipe?
- Can I substitute buttermilk in peanut butter cake?
- How do I know when the peanut butter sheet cake is done?
- Do I have to wait for the cake to cool before adding the frosting?
- Can peanut butter sheet cake be frozen?
- What is the difference between sheet cake and regular cake?
- How long does peanut butter sheet cake last at room temperature?
- Can I make this peanut butter sheet cake with cake mix instead?
- Related Recipes You May Also Like
- Wrapping Up This Peanut Butter Sheet Cake Recipe
- Peanut Butter Sheet Cake
Ingredients for Peanut Butter Sheet Cake
Before you start, gather everything you need. This easy peanut butter cake recipe uses a split ingredient list — one set for the cake batter and one for the fudgy peanut butter frosting that goes on top.
Sheet Cake Ingredients
- 2 cups (250 g) all-purpose flour
- 1 cup (200 g) granulated sugar
- 3/4 cup (150 g) light brown sugar, firmly packed
- 3/4 teaspoon baking soda
- 3/4 teaspoon salt
- 1 cup (237 ml) water
- 3/4 cup (177 g) unsalted butter, cut into pieces
- 1/4 cup (60 g) canola or vegetable oil
- 1/2 cup (145 g) creamy peanut butter
- 1/2 cup (118 ml) buttermilk (or substitute with milk plus 1/2 teaspoon vinegar)
- 2 large eggs, room temperature preferred
- 1 1/2 teaspoons vanilla extract
Fudgy Peanut Butter Frosting Ingredients
- 4 cups (500 g) powdered sugar (sift if lumpy)
- 1/2 cup (118 ml) buttermilk (or substitute with milk plus 1/2 teaspoon vinegar)
- 10 Tablespoons (150 g) unsalted butter, cut into pieces
- 2/3 cup (165 g) creamy peanut butter
- 1/4 heaping teaspoon salt
- 1 teaspoon vanilla extract
Why These Ingredients Matter
The ingredients in this peanut butter sheet cake with buttermilk are not random — each one plays a specific role, and understanding why helps you avoid common baking mistakes. Here is what you need to know before you measure a single cup of flour.
Use regular creamy peanut butter, not natural. Brands like Jif or Skippy contain stabilizers that keep the oils from separating, which means the peanut butter melts smoothly into both the batter and the boiled frosting. Natural peanut butter — the kind you have to stir — tends to separate when heated, leaving oily pockets and a greasy texture. I have tested this both ways, and the difference is night and day. Save the natural stuff for toast.
Unsalted butter plus measured salt gives you control. This is one of the most common questions I get from readers: why use unsalted butter if you are adding salt anyway? The answer is consistency. Salted butter varies wildly in salt content from brand to brand, and when you are making a dessert where salt balances sweetness, precision matters. Using unsalted butter and adding your own measured salt guarantees the same result every single time.
Brown sugar adds depth, baking soda adds lift. The combination of granulated sugar and light brown sugar gives the cake sweetness and a subtle molasses undertone that complements the peanut butter beautifully. Baking soda — not baking powder — is the leavener here because the buttermilk provides enough acid to activate it, creating a tender crumb without any bitter aftertaste.
Buttermilk is the secret to a tender crumb. Its acidity tenderizes the gluten in the flour, keeping the cake soft and springy. If you do not have buttermilk on hand, do not worry — I cover the best substitutes in the FAQ section below.
How to Make Peanut Butter Sheet Cake: Step-by-Step Instructions
Prep time: about 25 minutes | Bake time: 30 to 32 minutes | Total time: under 1 hour | Servings: 24 generous squares
This peanut butter cake from scratch comes together in two phases: the cake batter, which uses a hot liquid method, and the boiled frosting, which you make while the cake bakes. Follow these steps in order and you will have a flawless sheet cake every time.
Make the Cake Batter
- Preheat the oven to 350 degrees F (175 degrees C) and lightly grease a 13 by 9 baking pan. Set it aside while you prepare the batter.
- Whisk the dry ingredients. In a large bowl, combine the all-purpose flour, granulated sugar, light brown sugar, baking soda, and salt. Whisk until evenly distributed and no brown sugar lumps remain.
- Boil the wet mixture. In a medium saucepan, combine the water, butter pieces, and oil. Heat over medium heat, stirring occasionally, until the butter melts completely and the mixture comes to a rolling boil.
- Add the peanut butter. Remove the saucepan from the heat and stir in the creamy peanut butter. Keep stirring until it is completely dissolved and the mixture is smooth.
- Combine wet and dry. Pour the hot peanut butter mixture into the bowl with the dry ingredients and stir until just combined. Let the batter cool for 5 to 10 minutes so the eggs do not scramble in the next step.
- Mix the wet ingredients. In a separate bowl, whisk together the buttermilk, eggs, and vanilla extract until smooth.
- Finish the batter. Gradually stir the buttermilk mixture into the cooled batter, mixing until just combined. Do not overmix — a few small lumps are fine.
- Bake. Pour the batter evenly into your prepared 13 by 9 pan and transfer to the center rack of the preheated oven. Bake for 30 to 32 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs attached.
Baker’s tip: Ovens run hot or cold more often than you might think. If your cakes consistently bake faster or slower than recipes suggest, invest in an inexpensive oven thermometer. It is the single best way to fix uneven or unpredictable baking results.
Make the Fudgy Peanut Butter Frosting
Start the frosting while the cake is in the oven. Timing matters here — the frosting needs to be poured warm over the cake the moment it comes out of the oven. This is what creates that signature fudgy, candied texture that makes this recipe famous.
- Measure the sugar. Have your powdered sugar measured and ready. If it looks lumpy, sift it after measuring so your frosting stays silky smooth.
- Boil the frosting base. In a medium saucepan, combine the buttermilk, butter, creamy peanut butter, and salt. Cook over medium-low heat until the butter is fully melted. Increase the heat to medium and bring the mixture to a boil, stirring constantly. Remove from heat the moment it boils.
- Add sugar and vanilla. Immediately add the powdered sugar and vanilla extract. Whisk vigorously until the frosting is completely smooth and glossy.
- Frost the warm cake. Pour the frosting evenly over the cake while both the cake and the frosting are still warm. Use an offset spatula to spread it to the edges. Let the cake cool completely before slicing so the frosting has time to set.
Important: Do not wait for the cake to cool before adding the frosting. The warm cake absorbs some of the frosting, creating that melt-in-your-mouth texture that separates this recipe from every other peanut butter dessert. If the cake cools too much, the frosting will sit on top instead of soaking in slightly.
Delicious Topping and Serving Ideas
The classic peanut butter sheet cake frosting is phenomenal on its own, but sometimes you want to dress things up for a special occasion. Here are my favorite ways to customize this cake, whether you are serving it at a birthday party, holiday dinner, or casual potluck.
Topping Options
Chopped roasted peanuts add a satisfying crunch that contrasts with the soft, fudgy frosting. Sprinkle them on right after pouring the frosting so they stick as it sets. Roughly half a cup is plenty for the whole pan.
Mini chocolate chips are a no-brainer if you love the peanut butter and chocolate combo. Press them gently into the warm frosting and they will melt just slightly, creating little ribbons of chocolate throughout each bite.
Reese’s cup halves arranged in a grid pattern turn this into an instant birthday cake. Press them into the frosting while it is still warm so they settle in without sliding around.
Caramel drizzle adds a buttery sweetness that pairs beautifully with peanut butter. Warm store-bought caramel sauce for a few seconds in the microwave and drizzle it over the cooled cake just before serving.
Frosting Swaps
If you want a change from the fudgy boiled icing, there are several frosting options that work well. A classic peanut butter chocolate cake uses chocolate frosting, and you can use the same approach here — a simple chocolate buttercream or ganache turns this into a peanut butter chocolate sheet cake with almost no extra effort.
A peanut butter buttercream made with powdered sugar, softened butter, and creamy peanut butter gives a lighter, fluffier finish if the boiled frosting feels too rich for your taste. You can also halve the powdered sugar in the original frosting recipe if your family prefers a less sweet topping — many readers have told me this is their favorite adjustment.
Serving Suggestions
Serve this cake slightly warm with a scoop of vanilla bean ice cream for an unforgettable dessert. A dollop of fresh whipped cream also works, especially if you are cutting the sweetness of the frosting. For potlucks, cut the cake into 24 squares and arrange them on a platter — they hold their shape beautifully at room temperature and do not need refrigeration during the event.
This cake is sturdy enough to stack in a container for transport, which makes it my go-to for bake sales, family reunions, and neighborhood parties. Just layer parchment paper between rows of squares to keep the frosting from smudging.
Storage and Freezing Tips
One of the best things about this peanut butter sheet cake is how well it keeps. Unlike delicate layer cakes that wilt overnight, this cake actually tastes better on day two because the frosting continues to set and the flavors deepen.
Room Temperature Storage
Cover the cake pan tightly with plastic wrap or aluminum foil and leave it on the counter for up to 3 days. The cake stays moist at room temperature thanks to the oil and buttermilk in the batter, and the frosting firms up into a fudgy, sliceable layer. This is the method I recommend for most situations, especially if you are serving the cake at a party within a day or two of baking.
Avoid refrigerating the cake unless your kitchen is unusually warm. Refrigeration dries out the crumb and makes the frosting hard. If you do refrigerate it, bring the cake back to room temperature for at least an hour before serving so the texture softens.
Freezer Instructions
This peanut butter sheet cake freezes beautifully, which makes it perfect for make-ahead desserts. You can freeze it whole or cut into individual squares — I prefer squares because you can grab exactly what you need without thawing the entire pan.
To freeze, let the frosted cake cool completely. Then wrap the whole pan (or individual squares) in a layer of plastic wrap followed by a layer of aluminum foil. The double wrap prevents freezer burn and keeps the peanut butter flavor from absorbing other odors. Freeze for up to 3 months.
To thaw, transfer the wrapped cake to the refrigerator the night before you plan to serve it. Let it come to room temperature on the counter for about an hour before slicing. Individual squares thaw in about 30 minutes at room temperature.
Reheating
If you love the just-baked, warm-cake experience, reheat individual slices in the microwave for 10 to 15 seconds. The frosting will soften slightly and the cake will taste freshly baked. Do not microwave longer than 20 seconds or the edges will toughen up.
Pan Size and Recipe Variations
The standard recipe fills a 13 by 9 inch baking pan and serves about 24 people, but you can adapt this recipe to fit whatever pans you have. Here is a quick guide to the most common pan conversions.
Pan Conversion Guide
13 by 9 inch pan (standard): Bake at 350 degrees F for 30 to 32 minutes. This is the size this recipe was written for and produces the best results.
15 by 10 inch jelly roll pan: The batter spreads thinner, so check for doneness at 22 to 25 minutes. You will get thinner, wider slices that are perfect for feeding a large crowd.
Two 8-inch round pans: Pour the batter into two greased round pans for a layer cake. Bake for 25 to 28 minutes, then frost between the layers and on top. This makes a beautiful birthday cake.
Half recipe in an 8 by 8 inch pan: Cut all ingredients in half and bake for 20 to 25 minutes. Perfect for smaller households that do not need a full sheet cake.
Cupcakes: Line a muffin tin with paper liners and fill each cup about two-thirds full. Bake at 350 degrees F for 18 to 20 minutes. For a portable version, this batter also works beautifully in our peanut butter cupcakes recipe.
What Makes a Sheet Cake Different from a Regular Cake?
A common question from readers is what separates a sheet cake from a regular layer cake. The answer comes down to three things: the pan, the frosting method, and the texture. Sheet cakes are baked in a single shallow pan, frosted warm with a pourable boiled icing that sets into a fudgy layer, and served directly from the pan. Layer cakes are baked in multiple round pans, frosted with a spreadable buttercream, and removed from their pans before serving. The boiled frosting technique is what gives this peanut butter sheet cake its signature candied texture — you simply cannot replicate it with a traditional buttercream.
Flavor Variations
One reader favorite is adding half a cup of mini chocolate chips to the batter before baking — they melt into pockets of chocolate that complement the peanut butter perfectly. You can also swap the vanilla extract for maple extract for a warm fall flavor, or add a teaspoon of espresso powder to deepen the peanut butter taste without making the cake taste like coffee.
For a gluten-free version, substitute the all-purpose flour with your favorite 1-to-1 gluten-free baking blend and add an extra 1/2 teaspoon of baking powder. Readers with Celiac disease have confirmed this works beautifully. You can also substitute almond butter or sunflower seed butter for the creamy peanut butter, though the flavor will be noticeably different.
Pro Tips for the Best Peanut Butter Sheet Cake
These are the hard-won lessons from baking this cake dozens of times. Follow them and you will avoid every common pitfall.
Use a kitchen scale. Measuring flour by weight instead of volume is the single biggest upgrade you can make to your baking. A cup of flour can weigh anywhere from 120 to 150 grams depending on how you scoop it, and that difference is enough to turn a tender cake into a dry one. I highly recommend using the gram measurements provided in the ingredient list.
Prep everything before you start. This is called mise en place, and it means measuring all your ingredients, greasing the pan, and preheating the oven before you begin mixing. The hot liquid method moves quickly once you start, and having everything ready prevents rushed mistakes.
Let the batter cool before adding eggs. The hot liquid mixture needs 5 to 10 minutes to cool before you stir in the buttermilk and egg mixture. If the batter is too hot, the eggs will scramble and you will end up with bits of cooked egg throughout the cake.
Do not overmix. Once you combine the wet and dry ingredients, stir just until no dry flour remains. Overmixing develops the gluten in the flour and makes the cake tough instead of tender.
Check for doneness early. Every oven is slightly different, so start checking the cake at 28 minutes. Insert a toothpick into the center — if it comes out clean or with a few moist crumbs, the cake is done. If you want to be precise, an instant-read thermometer should register between 200 and 210 degrees F in the center.
Level your oven racks. If your cake rises unevenly on one side, your oven rack may be tilted. A simple fix is to slide a small piece of aluminum foil under the low side of the rack to level it out. This is a common issue that affects all baked goods, not just this recipe.
Equipment Guidance for Perfect Results
You do not need any specialty equipment for this recipe, but having the right tools makes the process smoother and the results more consistent. Here is everything I use when making this peanut butter sheet cake recipe.
A 13 by 9 inch baking pan is the foundation of this recipe. Metal pans conduct heat evenly and produce the best crust on the bottom and edges. Glass pans work too, but they retain heat longer, so you may need to reduce the oven temperature by 25 degrees and check for doneness a few minutes earlier. Whatever you use, grease it generously with butter or nonstick spray.
Two medium saucepans are needed — one for boiling the cake batter liquids and one for making the frosting. Using a 2-quart or 3-quart saucepan gives you enough room to whisk without splashing. If you only have one saucepan, wash it between the cake and frosting steps.
A set of mixing bowls in at least two sizes will keep you organized. You need one large bowl for the dry ingredients and batter, plus a smaller bowl for whisking the buttermilk and eggs together. Glass or stainless steel bowls work equally well.
An offset spatula makes spreading the warm frosting infinitely easier than a regular butter knife or rubber spatula. The angled blade lets you get right up against the edges of the pan without dragging your hand through the frosting.
A whisk is essential for getting the frosting smooth. The powdered sugar needs vigorous whisking to dissolve completely into the hot liquid, and a balloon whisk does this faster than a spoon. A hand whisk is plenty — you do not need an electric mixer for any part of this recipe.
An oven thermometer is optional but highly recommended. If your oven temperature is off by even 25 degrees, it can mean the difference between a perfectly baked cake and one that is dry or underdone in the center. Hang a cheap oven thermometer from the center rack and trust it over the dial.
A kitchen scale is the tool I recommend most often to home bakers. Weighing ingredients in grams eliminates the guesswork of measuring cups and gives you consistent results every time. The gram measurements in the ingredient list above are there for exactly this reason.
Common Questions Answered
Can I use natural peanut butter in this peanut butter sheet cake recipe?
I do not recommend it. Natural peanut butter separates when heated, which can leave oily pockets in the batter and frosting. Regular creamy peanut butter like Jif or Skippy contains stabilizers that keep the oils evenly distributed, producing a smooth, fudgy texture. Stick with conventional creamy peanut butter for the best results.
Can I substitute buttermilk in peanut butter cake?
Yes. The easiest substitute is to combine 1/2 cup of regular milk with 1/2 tablespoon of lemon juice or white vinegar. Let it sit for 5 minutes until it thickens slightly, then use it exactly as you would buttermilk. You can also use plain yogurt thinned with a little milk, or sour milk made the same way.
How do I know when the peanut butter sheet cake is done?
Insert a toothpick into the center of the cake. If it comes out clean or with a few moist crumbs attached, the cake is ready. For extra precision, use an instant-read thermometer — the internal temperature should register between 200 and 210 degrees F. Start checking at 28 minutes since oven temperatures vary.
Do I have to wait for the cake to cool before adding the frosting?
No, and you actually should not. The frosting should be poured over the cake while both are still warm. This allows the frosting to seep slightly into the cake, creating that signature fudgy texture. If you let the cake cool completely first, the frosting will just sit on top and will not set the same way.
Can peanut butter sheet cake be frozen?
Absolutely. Let the frosted cake cool completely, then wrap it tightly in plastic wrap followed by aluminum foil. You can freeze the whole pan or cut it into individual squares and freeze them separately. The cake keeps well in the freezer for up to 3 months. Thaw overnight in the refrigerator, then bring to room temperature before serving.
What is the difference between sheet cake and regular cake?
A sheet cake is baked in a single shallow pan, frosted warm with a pourable boiled icing that sets into a fudgy layer, and served directly from the pan. Regular layer cakes are baked in multiple round pans, frosted with spreadable buttercream, and removed from their pans before serving. The boiled frosting technique is what gives sheet cakes their unique candied texture.
How long does peanut butter sheet cake last at room temperature?
Covered tightly with plastic wrap or foil, this cake stays fresh at room temperature for up to 3 days. The oil and buttermilk in the batter keep it moist, and the fudgy frosting firms up as it sits. Avoid refrigerating it unless your kitchen is very warm, because refrigeration dries out the crumb.
Can I make this peanut butter sheet cake with cake mix instead?
You can, but the results will not match a from-scratch cake. If you want a shortcut, use a yellow or white cake mix and add 1/2 cup of creamy peanut butter to the batter along with an extra egg. The texture will be lighter and less rich, but the fudgy homemade frosting on top will still deliver that signature flavor.
Related Recipes You May Also Like
If you enjoyed this peanut butter sheet cake recipe, here are a few more desserts from the blog that you will love. If you love this recipe, you will also enjoy our chocolate chip sheet cake — same easy format, different flavor. Love peanut butter desserts? These Butterfinger cookies are another reader favorite.
Wrapping Up This Peanut Butter Sheet Cake Recipe
This peanut butter sheet cake recipe is proof that the best desserts do not require fancy techniques or hard-to-find ingredients. With a simple hot liquid method, a foolproof boiled frosting, and about an hour in the kitchen, you can produce a cake that feeds a crowd and disappears every time. Whether you are baking for a potluck, a holiday gathering, or a Tuesday night treat, this is the kind of recipe that becomes a family favorite.
Give it a try, and if you love it as much as my family does, check out our key lime cake for a bright, tangy alternative the next time you need an easy sheet pan dessert.
Peanut Butter Sheet Cake
Ingredients
Method
- Preheat oven to 350F (175C) and lightly grease a 13×9 baking pan. Set aside.
- In a large bowl, whisk together flour, sugars, baking soda, and salt.
- In a medium-sized saucepan, combine water, butter, and oil. Heat over medium heat, stirring occasionally until butter is melted and bring to a boil.
- Once boiling, remove from heat and add peanut butter. Stir until peanut butter is dissolved and mixture is smooth. Add to bowl with dry ingredients and stir until combined. Set aside to cool for 5-10 minutes.
- Meanwhile, in a separate bowl, whisk together buttermilk, eggs, and vanilla extract.
- Gradually stir buttermilk mixture into batter, stirring until just combined.
- Pour batter evenly into prepared pan and transfer to center rack of 350F (175C) preheated oven and bake for 30-32 minutes or until a toothpick inserted in the center comes out clean or with moist crumbs. Prepare frosting.
- Fudgy Peanut Butter Frosting: Measure out sugar and set aside (if you’re worried about lumps in your icing, sift the sugar after measuring).
- Combine buttermilk, butter, peanut butter, and salt in a medium-sized saucepan. Cook over medium-low heat until butter is melted. Increase heat to medium and bring to a boil while stirring constantly. Once boiling, remove from heat.
- Immediately add powdered sugar and vanilla extract.
- Whisk until smooth and immediately pour evenly over cake (in the pan, I do not remove my cake from the pan).