1Heat oven to 350°F (325°F for dark or nonstick pan). Line 9-inch square pan with foil so foil extends about 2 inches over sides of pan. Spray foil with cooking spray. Make brownies as directed on box for cakelike brownies, for 9-inch pan. Cool completely, about 1 1/2 hours.
2Remove from pan by lifting foil; peel foil away. Cut brownie in half; place 1 half on serving plate.
3Spoon frosting into microwavable bowl. Microwave uncovered on High 15 seconds. Stir frosting until smooth. Spread half of frosting over brownie half on plate. Place other half of brownie on top; pour remaining frosting over top. Sprinkle with candies. Refrigerate 30 minutes to set. Store loosely covered.