Line 8 x 8-inch square baking pan with aluminum foil, leaving an overhang on all sides, and spray the foil lightly with non-stick cooking spray.
Mix and bake the brownies according to box directions.
As soon as the brownies come out of the oven, top them the peanut butter cups and peanuts, distributing both evenly over the brownies.
In a medium heat-proof bowl, add the chocolate chips, peanut butter, and butter and cook for 30 seconds on 50% power. Give the mixture a stir and repeat heating and stirring until the chocolate chips have melted and everything is nice and smooth. Next, stir in the Rice Krispies Cereal until combined.
Pour the chocolate mixture over the top of the peanut butter cups and peanuts and gently smooth into an even layer. Cover with foil and chill in the refrigerator until firm, about 4 hours.
Use the foil overhang to lift the brownies from the pan. Cut into 16 squares and serve.
Notes
NOTE: Remember that you’ll also need whatever ingredients your favorite boxed brownie mix requires. Typically, this includes egg, oil, and/or milk, but your actual ingredients will vary.