**Prepare the Pan:** Line a 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal.
**Make the Peanut Butter Layer:** In a large bowl, combine melted butter, powdered sugar, peanut butter, and graham cracker crumbs. Mix until fully combined and smooth. Press the mixture evenly into the prepared pan, using a spatula or your hands to create a firm, even layer.
**Make the Chocolate Layer:** In a microwave-safe bowl, combine the chocolate chips and peanut butter. Microwave in 30-second intervals, stirring between each, until smooth and melted.
**Top the Peanut Butter Layer:** Pour the melted chocolate mixture over the peanut butter layer. Spread evenly with a spatula.
**Chill the Bars:** Refrigerate the pan for at least 2 hours or until the bars are firm and set.
**Cut and Serve:** Once set, lift the bars out of the pan using the parchment paper. Cut into squares or rectangles and serve chilled.