1/2 cup coarsely chopped chocolate-covered peanut butter cup candies
Heat oven to 350°F. Line 13 x 9-inch pan with foil so foil extends about 2 inches over sides of pan. Spray foil with cooking spray.
Make brownies as directed on package for 13 x 9-inch pan. Cool completely, about 1 1/2 hours. Remove from pan by lifting foil; peel foil away. Cut brownie in half lengthwise; place one half on serving plate.
Microwave frosting uncovered on High 20 seconds. Stir thoroughly or until smooth. Pour half of frosting over half of brownie on plate. Place other half of brownie on top; pour remaining frosting on top. Sprinkle with candies. Refrigerate 30 minutes to set. Store loosely covered.