Microwave 1 cup chocolate morsels in a 2-cup glass measuring cup at HIGH 1 minute, stirring after 30 seconds. Stir until smooth. Cool slightly.
Beat cake mix and next 3 ingredients at low speed with an electric mixer until moistened. Increase speed to medium, and beat 1 to 2 minutes or until well blended and smooth. Add melted chocolate and vanilla, beating until blended. Spoon batter by 1/4-cupfuls into paper baking cups in muffin pans.
Bake at 375° for 16 to 18 minutes or until a wooden pick inserted in center comes out clean. Let cool in pans on wire racks 5 minutes. Remove from pans, and cool completely on wire racks. Spread Orange Buttercream Frosting evenly over cupcakes.
Place remaining chocolate morsels in a 1-qt. zip-top plastic freezer bag; seal bag. Microwave at MEDIUM (50% power) 45 seconds to 1 minute, turning bag over after 30 seconds. Squeeze chocolate in bag until smooth. Cut a tiny hole in 1 corner of bag. Pipe melted chocolate over Orange Buttercream Frosting on cupcakes by gently squeezing bag.