Line Pan: Line a 9×9-inch square baking pan with parchment paper, leaving overhang on the sides for easy removal.
Mix Peanut Butter Layer: In a medium bowl, combine melted butter, graham cracker crumbs, powdered sugar, and peanut butter. Stir until well combined and mixture is thick.
Press into Pan: Pour the peanut butter mixture into the prepared pan. Press down firmly with your hands or the back of a spoon to create an even layer.
Melt Chocolate: Place chocolate chips in a microwave-safe bowl. Microwave in 30-second intervals, stirring between each, until completely melted and smooth (about 1-1.5 minutes total).
Add Chocolate Topping: Pour melted chocolate over the peanut butter layer. Spread evenly with a spatula to cover the entire surface.
Chill: Refrigerate for at least 1 hour until the chocolate is firm and set.
Cut and Serve: Using the parchment paper overhang, lift the bars from the pan. Cut into 16 squares with a sharp knife. Store in the refrigerator.