Spray a small baking dish or muffin tin with non-stick spray. Set aside.
Combine melted butter, Graham cracker crumbs, powdered sugar, peanut butter, and brown sugar. Mix together until combined. Add in 1/2 of the Reese's Pieces and stir together.
Spread evenly in the bottom of the baking dish or muffin tin.
Chocolate topping: In a microwave safe bowl, add chocolate chips and peanut butter and microwave in 15 seconds intervals until fully melted.
Spread the chocolate topping over top of the peanut butter mixture evenly. Sprinkle with mini Reese's pieces.
Place in the refrigerator to firm up for about 30 minutes
Cut into bars or gently remove from the muffin tin and enjoy.