1. Preheat your oven to 350°F (175°C). Grease and flour a 15×10-inch sheet pan.
2. In a large bowl, whisk together flour, sugar, baking soda, and salt.
3. In a saucepan over medium heat, melt the butter. Stir in water and bring the mixture to a boil. Once boiling, remove from heat and stir in 1 cup of peanut butter until smooth. Cool slightly.
4. To the peanut butter mixture, add the buttermilk, eggs, and vanilla extract, mixing until everything is incorporated.
5. Gradually add the peanut butter mixture to the flour mixture and stir until combined. The batter will be pretty thick—that’s totally normal.
6. Pour the batter into the prepared sheet pan, spreading it out evenly.
7. Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
8. While the cake is baking, make the frosting. In a saucepan, combine 1/2 cup butter, 2/3 cup peanut butter, and milk. Heat until the butter and peanut butter melt and the mixture is smooth, stirring occasionally.
9. Remove from the heat and gradually mix in the powdered sugar and vanilla extract until the frosting is smooth and creamy.
10. Once the cake is done and while it’s still warm, pour the frosting over the cake and spread it out evenly. Allow the cake to cool, letting the frosting set.
Variations & Tips
– For a slightly healthier version, you can swap half of the all-purpose flour for whole wheat flour. It’ll add a nutty flavor that pairs well with the peanut butter.
– Not a fan of super sweet? Reduce the sugar in the cake batter by 1/4 cup to dial down the sweetness a hair.
– To get that flawless cake-to-frosting ratio, make sure your cake is warm when you spread the frosting. It’ll glide right on and seep into every crevice for the ultimate peanut butter experience.
– For a little crunch, sprinkle chopped peanuts on top of the frosting before it sets.
– If you happen to have leftovers, though I doubt you will, this cake keeps beautifully in an airtight container at room temperature for up to 3 days, making it perfect for meal prepping dessert for the week (if you’re into that sort of thing).
– Have an allergy in the family? Swap out the peanut butter for almond or cashew butter for an equally delicious but allergy-friendly option!
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Bake this Peanut Butter Sheet Cake next time you’re craving something sweet and nutty. It’s a crowd-pleaser that’s almost too easy to make—don’t worry, I won’t tell if you won’t. 😉 Enjoy!
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