Step 1

Preheat the oven to 350˚F. Generously grease and flour a 13x18-inch sheet pan

Step 2

Combine water, butter, and peanut butter in a medium saucepan. Heat until mixture comes to a boil while stirring constantly. Remove from heat and add the sugars, flour, salt, and baking soda, whisk until lump-free then add eggs, buttermilk, and vanilla whisk until well combined.

Step 3

Pour the batter into the prepared pan, smooth with a spatula to an even layer. Bake for 15 minutes or until a toothpick inserted in the center comes out clean.

Step 4

When the cake comes out of the oven, prepare the frosting. *see notes

Step 5

In a small saucepan, melt butter then add milk and cocoa powder. Bring to a boil. Remove from the heat. Whisk in powdered sugar and vanilla until smooth. Pour icing over warm cake. Cool completely on a wire rack before serving.