1. Preheat the oven to 350°F and grease two 8 inch round cake pans. Line the bottoms with parchment paper.

2. In a large bowl, whisk together the flour, cocoa powder, granulated sugar, brown sugar, baking powder, baking soda, and salt.

3. Add the eggs, buttermilk, vegetable oil, and vanilla extract. Mix until combined.

4. Slowly pour in the hot coffee or hot water and stir until the batter is smooth.

5. Divide the batter evenly between the prepared pans.

6. Bake for 28 to 32 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

7. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

8. To make the frosting, beat the butter until smooth. Add the peanut butter and beat again until creamy.

9. Gradually mix in the powdered sugar, then add the vanilla extract, salt, and enough heavy cream or milk to create a fluffy spreadable frosting.

10. Place one cake layer on a serving plate and spread frosting over the top.

11. Add the second cake layer and frost the top and sides of the cake.

12. Finish with chopped peanuts or chocolate shavings if desired. Chill briefly before slicing for cleaner pieces.