Line a 9x9 inch baking dish with parchment paper, leaving some overhang for easy removal.
In a large mixing bowl, combine melted unsalted butter and Ritz cracker crumbs. Stir until coated.
Add powdered sugar and 3/4 cup peanut butter to the mixture and mix until well combined and thick.
Transfer mixture to the prepared baking dish and press down evenly with a spatula, packing tightly.
Sprinkle chopped miniature Reeses Peanut Butter Cups evenly over the pressed mixture and gently press down.
Melt chocolate chips in a microwave-safe bowl in 30-second intervals, stirring until smooth.
Stir remaining 2 tablespoons peanut butter into melted chocolate until well combined.
Pour chocolate-peanut butter mixture over the crust and Reeses Cups; spread evenly with a spatula.
Sprinkle Reeses Pieces on top of the melted chocolate, pressing gently to adhere.
Refrigerate bars for at least 2 hours until firm and set. Use parchment overhang to lift bars out.
Slice bars into squares with a sharp knife and serve immediately or store in an airtight container in the refrigerator.