Step 1

Preheat the oven to 350 degrees Fahrenheit. Grease and flour a 9x13-inch baking pan.

Step 2

In a large bowl, combine flour, sugars, baking soda, and salt. Set aside.

Step 3

In a saucepan over medium heat, combine the butter and water. Bring to a boil, then remove from the heat, add the peanut butter, and stir until well blended.

Step 4

Pour the peanut butter blend over the dry ingredients and mix until well combined.

Step 5

In a small bowl, whisk the buttermilk, eggs, and vanilla until smooth. Add to the batter and mix until smooth.

Step 6

Pour the batter into the prepared baking pan, spreading evenly, and bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.

Step 7

While the cake cools, make the frosting. Combine the butter, peanut butter, and milk in a saucepan over medium heat and bring to a boil.

Step 8

Remove from the heat and gradually stir in powdered sugar and vanilla until smooth.

Step 9

Immediately spread the frosting over the warm cake. Then, let the cake and frosting cool before slicing. Serve and enjoy!