1In a large mixing bowl, combine the melted butter, graham cracker crumbs, powdered sugar, and peanut butter. Mix until smooth and well combined.
2Line an 8x8-inch or 9x13-inch baking dish with parchment paper and press the peanut butter mixture evenly into the bottom of the dish.
3In a microwave-safe bowl, combine the chocolate chips and peanut butter and microwave in 20-second intervals, stirring after each, until the mixture is fully melted and smooth.
4Pour the melted chocolate mixture over the peanut butter base and spread it evenly with a spatula.
5Refrigerate the bars for at least 2 hours, or until the chocolate is firm and the bars are fully set.
6Remove the bars from the pan using the parchment paper and slice into squares or rectangles.