Place about 1 ½ teaspoons peanut butter filling on top of batter. Then, do your best to push the filling down into the batter. (Unlike my photo where it is just sitting on top.) If you don’t push the filling into the middle, it may slide over while it bakes, that is what mine did.
2Bake for about 18 minutes, or until an inserted knife comes out clean.
Buttercream: Beat butter and cream cheese. Add remaining ingredients and adjust as needed to reach desired consistency.
Pipe onto cooled cupcakes and top with half of a peanut butter cup. (To cut easily, put peanut butter cups into the freezer for a few minutes.)