Bake the brownies according to package directions in a 9×9 pan lined with foil.
During last 5 minutes of baking, remove from oven and sprinkle chopped peanut butter cups and chopped peanuts on top. Return to oven for remaining 5 minutes to melt the chocolate.

As soon as you pull them out of the oven, spread the melty peanut butter cups/peanuts with an off-set spatula to smooth over top. Let brownies cool.
Next in a microwave safe bowl combine chocolate chips, peanut butter and butter. Heat in microwave for 1 minute, stirring when done. If needed, continue heating in 20 second increments until chocolate chips are melted.
Stir in cereal, vanilla and salt until evenly combined.
Pour over brownies and smooth. Chill until chocolate is set, about 2 hours.
Cut into squares to serve

Notes
Store airtight for up to 3 days. You can store these at room temperature or in refrigerator.