01 - Line a 9x9-inch baking dish with parchment paper, leaving an overhang on the sides for easy removal.
02 - In a medium bowl, combine the melted butter and 1 cup peanut butter until smooth. Add the powdered sugar and graham cracker crumbs, stirring until well blended and a thick dough forms.
03 - Press the peanut butter mixture evenly into the prepared baking dish, smoothing the top with a spatula.
04 - In a microwave-safe bowl, combine the chocolate chips and remaining 1/4 cup peanut butter. Microwave in 20-second intervals, stirring after each burst, until completely melted and smooth.
05 - Pour the melted chocolate mixture over the peanut butter base, spreading it into an even layer.
06 - Refrigerate the bars for at least 2 hours, or until the chocolate topping is set and firm to the touch.
07 - Lift the chilled slab out of the pan using the parchment overhang. Cut into 16 even squares using a sharp knife.