1. Preheat the oven to 350°F 175°C. Grease a 9×13 inch baking pan with nonstick spray or butter and line the bottom with parchment paper if desired.

2. In a medium bowl whisk together the flour baking powder baking soda and salt until well combined then set aside.

3. In a large mixing bowl beat the melted slightly cooled butter creamy peanut butter and granulated sugar together until smooth thick and slightly lighter in color.

4. Add the eggs one at a time mixing well after each addition then beat in the vanilla extract until the batter looks smooth and glossy.

5. With the mixer on low speed add about one third of the dry ingredients to the peanut butter mixture then pour in about half of the buttermilk and mix just until combined. Repeat with another third of the dry ingredients the remaining buttermilk and the final third of the flour mixture stopping as soon as no streaks of flour remain.

6. Spread the batter evenly into the prepared pan smoothing the top with a spatula. Bake for 28 to 32 minutes or until the top springs back lightly when touched and a toothpick inserted in the center comes out clean or with just a few moist crumbs.

7. Transfer the pan to a wire rack and let the cake cool completely in the pan before adding the frosting.

8. To make the frosting beat the softened butter and creamy peanut butter together in a large bowl until very smooth and fluffy.

9. Gradually add the powdered sugar about 1/2 cup at a time mixing on low speed after each addition so it does not puff out of the bowl.

10. Add the heavy cream or milk vanilla extract and salt then increase the mixer speed and beat until the frosting is light creamy and spreadable adding an extra splash of cream if it is too thick or a little more powdered sugar if it is too thin.

11. Spread the frosting evenly over the cooled cake using a spatula to create swoops and swirls.

12. Sprinkle the chopped roasted peanuts evenly over the top of the frosted cake then slice into squares and serve.