PREHEAT oven to 350° F (325° F for dark or nonstick pan). Grease 12-inch pizza pan. Make brownie batter as directed on package. Spread onto prepared pan. Sprinkle 1 cup morsels over top of batter.
BAKE for 20 to 24 minutes or until toothpick inserted about 2 inches from center comes out almost clean. Cool completely in pan on wire rack.
FROST with frosting, leaving a border around the edge. Sprinkle with remaining 2/3 cup morsels and sprinkles over frosting.