In a large pot melt butter over medium heat. Add marshmallows and turn heat to low. Stir until completely smooth. Remove from heat and quickly stir in peanut butter. Add cereal.
Fold in the mini marshmallows. Pour rice krispies into a 9-inch square baking dish lined with parchment paper or buttered foil. Do not press them in tightly. Just very gently even the top of the treats. I use the buttered paper or marshmallow bag wrapper to press it down.
Top the melted peanut butter morsels with the peanut butter cups. Press these in so they stick. Allow to set 1 hour. Cut into squares and store in a airtight container.