Bake brownies according to package directions in a 9x9 pan sprayed with nonstick spray.
While brownies are baking measure chocolate chips, peanut butter and cereal. Also, chop peanut butter cups and chop peanuts if needed. Having these ready when the brownies come out of the oven makes it easier!
During last 5 minutes of baking, remove from oven and sprinkle chopped peanut butter cups and chopped peanuts on top. Return to oven for 5 minutes to melt chocolate.
Remove from oven and immediately spread the warm peanut butter cups/peanuts with baking spatula or back of a spoon smooth. Let brownies cool.
In a microwave safe bowl combine chocolate chips, peanut butter and butter. Heat in microwave for 1 minute; stir. Heat additional 20 seconds at an time until chocolate chips are melted.
Stir in cereal, vanilla and salt until evenly combined.
Pour over brownies and smooth. Chill until chocolate mixture on top is set, about 2 hours.
Cut into squares to serve.