1Heat oven to 350°F. Make and bake brownies as directed on box, using butter, eggs and any of the pan choices—except line pan with foil, then grease foil on bottom only for easier removal. Cool completely, about 1 hour.
2Spread frosting over brownies. Sprinkle with peanuts. Refrigerate.
3In medium microwavable bowl, microwave chocolate chips and peanut butter uncovered on High 1 to 2 minutes, stirring once, until melted. Stir in cereal. Spread over frosted brownies. Cool completely before cutting, about 1 hour. Cut into 4 rows by 4 rows. Store tightly covered at room temperature.