Preheat oven to 350?F. Grease two 8-inch round baking pans and line the bottoms with parchment paper.

Stir together sugar, flour, cocoa, baking powder, baking soda, and salt in a large bowl.

Add eggs, buttermilk, oil, and vanilla and beat on medium speed for about 2 minutes. Stir in the boiling water (the batter will be very thin).

Pour batter into prepared cake pans.

Bake for about 30 to 35 minutes or until a toothpick inserted in the center comes out clean. Allow to cool in the pan for 10 minutes; remove from pans to wire racks and cool completely.

Once cakes have cooled, use a sharp serrated knife to cut each cake horizontally in half, resulting in four thin cake rounds.

Place one cake layer on a serving plate. Smooth ? of the peanut butter frosting on top. Repeat with the remaining cake layers, adding peanut butter frosting between each layer of cake.

For the chocolate frosting, add melted butter to a large mixing bowl and stir in cocoa powder. Add powdered sugar, milk, and vanilla and beat until smooth. Adjust consistency with more powdered sugar or milk as needed.

Spread the chocolate frosting evenly over the outside of the cake. Optional: Pipe swirls of extra chocolate and peanut butter frosting on top and add mini Reese's cups.