Preheat and Prepare: Preheat your oven to 350°F (175°C). Grease and flour two round cake pans.
Mix Dry Ingredients: In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add Wet Ingredients: To the dry ingredients, add the eggs, milk, vegetable oil, and vanilla. Mix on medium speed for about 2 minutes until well combined.
Incorporate Boiling Water: Carefully stir in the boiling water until the mixture is smooth; it will be a bit thin, but that's okay!
Bake the Cakes: Pour the batter into the prepared pans and bake for 30-35 minutes, or until a toothpick comes out clean.
Cool: Once baked, let the cakes cool in the pans for 10 minutes before transferring them to wire racks to cool completely.
Make the Frosting: Beat together the peanut butter, powdered sugar, softened butter, and vanilla extract until fluffy. Gradually add the heavy cream until desired consistency is reached.
Assemble the Cake: Place one layer of cake on a serving plate, spread a layer of frosting over the top, add the second cake layer, and frost the entire cake.
Decorate: Top the cake with chopped peanut butter cups for that ultimate overload!
Enjoy: Slice it up and serve! Don’t forget to share with friends and family.