Preheat oven to 350 degrees. Line cupcake pans with paper liners.
Combine all ingredients into large mixing bowl. Mix at low speed for 30 seconds, and scrape bowl. Mix at high speed for 3 minutes.
2Fill liners 1/2 to 2/3 full of batter. If adding a filling, see below. Bake 20 to 25 minutes or until toothpick inserted in center comes out clean.
3Cool 10 minutes in pans then remove from pan, and place on wire racks to cool completely.
Frost when chocolate cupcakes are completely cool.
4For the Filling:
For the ganache filling, place chocolate, cream, and confectioners' sugar in a small microwave-safe bowl. Cook on high power until mixture is warm to the touch, 20-30 seconds. Whisk until smooth and transfer to the refrigerator. Let stand until just chilled, no longer than 30 minutes.Divide batter evenly among muffin pan cups, filling each 3/4 full. Place one slightly rounded teaspoon of the ganache filling on top of each cupcake.
Cream the butter until light and fluffy. Slowly add in the sugar.
Add the vanilla and cream.
Beat in the peanut butter until creamy.
Frost the cupcakes as desired. Top with half a Reese’s Peanut Butter Cup.