01 - Line a 9x9-inch baking dish with parchment paper, leaving an overhang on two sides for easy removal.
02 - In a medium bowl, combine the melted butter and 1 cup creamy peanut butter, stirring until completely smooth. Add the sifted powdered sugar and graham cracker crumbs, then mix thoroughly until a thick, uniform dough forms.
03 - Transfer the mixture to the prepared baking dish and press it firmly into an even layer, smoothing the surface with a spatula.
04 - Place the chocolate chips and remaining 1/4 cup peanut butter in a microwave-safe bowl. Microwave in 20-second intervals, stirring between each burst, until the mixture is fully melted and glossy.
05 - Pour the melted chocolate mixture over the peanut butter base, spreading it into an even layer with a spatula.
06 - Refrigerate the bars for at least 2 hours, or until the chocolate topping is completely set and firm to the touch.
07 - Lift the slab out of the dish using the parchment overhang. Place on a cutting board and slice into 16 even squares. Store any leftovers in an airtight container in the refrigerator.