Preheat oven to 350. Line 24 muffin tins with cupcake liners. Place a peanut butter cup (regular size) in the bottom of each tin. Prepare cake mix according to package instructions. Fill each cupcake liner ¾ full. Bake for 18-22 minutes.
Once the cupcakes have cooled, prepare the frosting. Cream together the peanut butter and butter. Add the powdered sugar ½ cup at a time until well combined. Add the milk to reach the desired creaminess and texture for the frosting. I used a Ziplock bag to pipe the frosting onto the cupcakes.
To garnish, cut miniature peanut butter cups in half and place on top of each cupcake.
Recipe by Five Wooden Spoons at https://www.fivewoodenspoons.com/2013/03/06/peanut-butter-cup-cupcakes/