1Heat oven to 350°F. Line 13x9-inch pan with foil so foil extends about 2 inches over sides of pan. Spray foil with cooking spray. Make and bake brownies as directed on box for 13x9-inch pan, using water, oil and eggs. Cool completely, about 1 hour.
2Remove brownies from pan by lifting foil; peel foil from sides of brownies. Using 2 1/2-inch star-shaped cookie cutter, cut brownies. Place frosting in resealable food-storage plastic bag; seal bag. Cut off one bottom corner of bag. Pipe frosting on star-shaped brownies. Sprinkle with decors.