1Heat oven to 350°F (325°F for dark or nonstick pans). Place Reynolds Mini Designer Baking Cups in each of 48 mini muffin cups.
2Make cupcake mix as directed on box, using water, oil and eggs. Fill muffin cups one-third full. Squeeze filling pouch 20 times; cut off corner of pouch at cut line. Divide filling evenly among cupcakes, making sure filling does not touch sides of muffin cups. Place 1 peanut butter cup candy in center of each cupcake. Evenly distribute remaining batter among cupcakes, making sure filling is completely covered. Bake 18 to 20 minutes or until tops are set. Cool 10 minutes; remove cupcakes from pans to cooling racks. Cool completely.
3In small microwavable bowl, microwave chocolate chips on High 30 to 60 seconds, stirring once, until smooth; cool. In large bowl, mix powdered sugar, butter and peanut butter with electric mixer on low speed until frosting is smooth. Add melted chocolate until just combined. Pipe or spread frosting on cupcakes. Sprinkle with peanut butter pieces.