PREHEAT oven as directed for cupcakes. Paper-line 24 muffin cups. PREPARE cake batter according to package directions. Spoon into prepared muffins cups. Bake as directed or until wooden pick inserted in cupcakes comes out clean. Cool in pans for 5 minutes; remove to wire racks to cool completely. BEAT butter and cocoa in large mixer bowl until creamy. Add powdered sugar and vanilla extract; beat on low until combined. Slowly beat in 4 tablespoons milk until creamy, adding additional tablespoons of milk if needed. Remove 1 cup of frosting to small bowl. Stir in ½ cup chopped DelightFulls morsels. Spoon filling mixture into pastry bag fitted with large pastry tip or into food storage bag with ½-inch snipped from corner of bag. CUT a 1-inch circle 1-inch deep with sharp knife from each cupcake. Carefully remove cake pieces and save for another use such as crumbling over ice cream. Pipe filling mixture into each cupcake. Filling should be level with top of cupcake. FROST cupcakes with remaining frosting in bowl. Sprinkle cupcakes with remaining ½ cup chopped DelightFulls morsels.