PREPARE cake batter and bake as directed on package for 24 cupcakes. Cool in pans 15 min. Remove from pans to wire racks; cool completely.
FROST cupcakes with Cool Whip. Top each with 2 cookies for the music notes.
POUR chocolate into resealable plastic bag. Cut off 1 small corner from bottom of bag. Squeeze chocolate from bag to add stems of music notes. Keep refrigerated.