Preheat oven to 350F (175C) and line two 12-count cupcake tins with paper liners. Set aside.

In a large mixing bowl, whisk together flour, sugars, baking powder, baking soda, and salt.

Add melted butter and oil and use an electric mixer to stir until all flour is moistened.

Stir in peanut butter.

Add eggs, vanilla extract and sour cream and stir until thoroughly combined.

Slowly drizzle in milk and stir until completely combined and batter is smooth and uniform.

Evenly divide batter into prepared cupcake tin.

Transfer to center rack of 350F (175C) oven (I only bake one tray at a time) and bake for 22-24 minutes or until a toothpick inserted in the center comes out clean or (preferably) with moist crumbs. Cupcake surfaces will crack, the cracks may still appear wet when the cupcakes are finished baking. Do not over-bake or cupcakes will be dry and crumbly.

Allow cupcakes to cool in pan for 5 minutes before gently, carefully removing to a cooling rack to cool completely before frosting.

Peanut Butter Chocolate Swirled Frosting & Decorating

Combine butter, peanut butter, vanilla extract and salt and stir until smooth and creamy.

Gradually add powdered sugar until completely combined. Thin frosting as needed by adding milk, one tablespoon at a time, until smooth and creamy.

Measure out approximately half of the frosting into a disposable piping bag and set aside.

Add cocoa powder to remaining half of frosting and stir until completely combined. If needed, thin the frosting with additional milk.

Transfer chocolate frosting to another piping bag. Snip the ends off both frosting bags and place in an additional piping bag that’s been fitted with a large closed star piping tip (I use Ateco 848) together. Pipe swirled frosting onto cupcakes (note that the first bit you pipe may not be swirled but as both frostings work their way through you’ll get a nice swirl!).