Peanut Butter Sheet Cake is a moist sheet cake topped with a super creamy and sweet peanut butter icing. It is a peanut butter lover’s dream and perfect for potlucks and picnics. The cake is so fluffy and moist with just the right amount of peanut butter flavoring. The frosting is the real show stopper on this peanut butter sheet cake, though. You don’t need to be able to frost a cake or worry about anything like that. The frosting will even itself out with just a couple swooshes from your knife.
And since cakes rise in the center, gravity works to push the frosting out to the lower edges of the cake. This is definitely a dessert where you want to go for the edges. You get so much more peanut butter frosting. Just be sure to sift your powdered sugar before you add it to the cooked peanut butter. If you don’t, you’ll end up with little clumps in your frosting. With peanut butter in the cake batter and the icing, there’s plenty of peanut butter flavor in this peanut butter sheet cake.
Both the cake batter and the frosting start with ingredients that come to a boil on the stove. If you’ve never had a peanut butter sheet cake, you really need to make a traditional one, too. It’s good stuff. Once your cake is baked and still slightly warm, that’s when you pour on the frosting so it stands up on the cake, but you can make it however you prefer.
For the cake;
- 1 cup butter
- 1 cup of water
- 1/2 cup unsweetened cocoa powder
- 2 cup all-purpose flour
- 1 tsp. baking soda
- 1/4 tsp. kosher salt
- 2 large eggs, at room temperature
- 1 cup of sugar
- 1/2 cup packed light brown sugar
- 2 tsp. pure vanilla extract
- 1/2 cup buttermilk, at room temperature
For the Frosting;
- 1/2 cup butter, at room temperature
- 1 1/2 cup creamy peanut butter
- 3 cup powdered sugar
- 1/2 cup heavy cream
- 1 tsp. pure vanilla extract
- pinch of salt
- Melted creamy peanut butter, for drizzling
- Chopped peanut butter cups, for topping
- Mini chocolate chips, for topping
- Preheat oven to 350°. Generously grease a 12″-x-17″ half sheet/jelly roll pan and set aside.
- In a large saucepan over medium heat, heat butter, water, and cocoa powder. Whisk constantly until butter has melted and everything is smooth and combined, then set aside.
- In a large bowl, whisk together flour, baking soda, and salt. Pour warm chocolate-butter mixture on top, then slowly whisk together until combined.
- Whisk eggs and sugars together in a medium bowl. Whisk in vanilla until combined, then pour into chocolate batter and whisk until combined.
- Finally, whisk in buttermilk, then pour chocolate batter into the prepared sheet pan.
- Bake 18 to 20 minutes, or until a toothpick stuck into the cake comes out clean. Remove cake from oven and set the pan on a wire rack.
- Let cake cool completely in pan before frosting.
- In a large bowl using a hand mixer or in the bowl of a stand mixer using the whisk attachment, beat butter and peanut butter together on medium-high speed for 2 minutes until completely smooth and creamy.
- Add powdered sugar, cream, vanilla, and salt. Beat on low speed about 20 seconds, then gradually increase to high speed.
- Beat on high 1 minute until combined and fluffy. Taste; add more salt if needed.
- Spread frosting over cooled cake, then drizzle with melted peanut butter and top with peanut butter cups and mini chocolate chips.
- Slice and serve. Cover leftovers tightly and store in the refrigerator for up to 5 days.