This Peanut Butter Sheet Cake is an unbelievably moist, rich, peanut butter cake with creamy peanut butter frosting poured on top. Similar to Texas Sheet Cake, but for the peanut butter lover instead!
Preheat oven to 375 degrees F. Line a cookie sheet 12x18-inch (sheet pan size) with parchment paper. Set aside.
In a LARGE saucepan, combine peanut butter, water, and butter for the cake. Bring to a boil, while stirring constantly. Once boiling, remove from heat. Add in sugars, flour, salt and baking soda. Mix until well combined. Add in eggs, buttermilk, and vanilla until blended. Pour into prepared baking sheet and bake for 15 minutes.
While the cake is baking, prepare the frosting. In a saucepan, combine butter, buttermilk, and peanut butter. Bring to a boil, while stirring.
Remove from heat and add in powdered sugar and vanilla extract. Whisk until smooth. Pour over warm cake.
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Notes
Don't have buttermilk handy? You can make a buttermilk substitute to use in this recipe.
Unsalted butter is my preference here (and for most cakes and frostings). If you only have salted butter that will work, too, just reduce the amount of salt called for in the recipe.