01 - Line a 9x13-inch baking dish with parchment paper, leaving enough overhang on the sides to lift the bars out later.
02 - In a large mixing bowl, stir together the creamy peanut butter and melted unsalted butter until completely smooth and well blended.
03 - Fold in the graham cracker crumbs and powdered sugar, stirring until the mixture is uniform and no dry pockets remain.
04 - Transfer the mixture to the prepared baking dish and press it firmly into an even, flat layer using a spatula or your hands.
05 - In a microwave-safe bowl, combine the semi-sweet chocolate chips and peanut butter. Microwave in 30-second intervals, stirring between each burst, until fully melted and silky smooth.
06 - Pour the melted chocolate mixture over the peanut butter base and spread it into an even layer using a spatula.
07 - Refrigerate the bars for at least 2 hours, or until the chocolate topping is firm and set completely.
08 - Lift the slab out of the dish using the parchment paper overhang, cut into 16 even bars, and serve chilled.