Preheat oven to 350F (175C) and thoroughly grease and flour the sides of three 8” cake pans, tapping out any excess flour, and line the bottoms with parchment paper.

In a large bowl (or the bowl of your stand mixer fitted with the paddle attachment), combine flour, sugar, baking powder, baking soda, and salt.

With mixer on low speed, add softened butter one Tablespoon at a time, allowing each Tablespoon to be fully incorporated into the dry ingredients before adding the next. Once all butter is added, the mixture will have a sandy, crumbly texture.

Add oil and lime zest and stir until well combined. Set aside.

Add the key lime juice to a large measuring cup (at least 2-cup), then add the milk until it reaches the 1 ½ cup line and whisk to combine.

Add eggs and vanilla to the milk mixture and whisk to combine.

Turn mixer to low speed and slowly add the milk mixture into batter until fully combined, pausing to scrape the sides and bottom of the bowl as needed. Batter should be uniform, silky and smooth.

Evenly divide batter into prepared pans (if weighing batter, each pan should have approximately 460 grams of batter) and bake in the center rack of preheated 350F (175C) oven for 26-28 minutes, or until a toothpick inserted in the center of each cake comes out clean or with a few moist crumbs.

Allow cakes to cool in their pans for 10-15 minutes, then run a knife along the edge of the pan to loosen from the edges and carefully invert onto a cooling rack to cool completely. While cakes are cooling, prepare your frosting.

In a small, non-reactive saucepan (see note) whisk together egg yolks, key lime juice, sugar, and salt.

Add butter and cook over medium/low heat, whisking constantly until mixture is thickened. This will take several minutes; once it is thickened the whisk should start to leave trails through the curd, and it should coat the back of a spoon.

Pour curd through a fine mesh strainer into a heatproof bowl. Allow to cool completely before proceeding (this may be placed in the refrigerator to cool faster).

In a large mixing bowl, use an electric mixer to beat softened butter and cream cheese until smooth and creamy.

Gradually add 4 cups (500g) of powdered sugar until completely incorporated.

Add the cooled curd, one Tablespoon at a time, until you’ve added 5-6 Tablespoons. Be sure to scrape the sides and bottom of the bowl to be sure all ingredients are thoroughly combined. If the frosting seems too soft, too tart, or on the verge of breaking add the remaining sugar as needed.

Once cakes are cooled, level the tops if necessary.

Frost each layer evenly with the prepared frosting. Evenly frost the outside of the cake with the remaining frosting.

Gently press graham cracker crumbs around the bottom of cake, about a quarter of the way up.

Pipe, swirl, or dollop stabilized whipped cream frosting over the top of the cake, if using. Decorate with additional graham cracker crumbs or lime zest, if desired.

Allow to chill in the refrigerator for at least 30 minutes before cutting and serving. Enjoy!