Chocolate Chocolate Peanut Butter Cupcakes

Heat oven to 350º F. Line 12 muffin cups with paper baking cups. In large bowl, combine all cupcake ingredients, except peanut butter cups. Stir just until blended. Fill muffin cups about 3/4 full. Press peanut butter cup into center of each until even with batter Bake at 350º F. for 20 to 25 minutes or until edge of cupcake springs back when lightly touched. Cool in pan 10 minutes; remove to wire rack; cool completely. Cream together peanut butter and butter. Beat in sugar, vanilla and milk to spreading consistency. Spread over cool cupcakes.