In a large mixing bowl, combine the melted butter, graham cracker crumbs, powdered sugar, and 1 ½ cups peanut butter. Stir until fully blended and smooth.
Press the mixture evenly into the bottom of a 9x13-inch pan lined with parchment paper.
Prepare the Chocolate Layer:
In a microwave-safe bowl, combine the chocolate chips and ¼ cup peanut butter. Microwave in 30-second intervals, stirring between each interval, until the mixture is fully melted and smooth.
Assemble the Bars:
Pour the melted chocolate mixture over the peanut butter base, spreading it evenly with a spatula.
Chill and Set:
Refrigerate the pan for at least 2 hours, or until the chocolate layer is firm.
Cut and Serve:
Once chilled, remove the pan from the refrigerator. Lift the bars out using the parchment paper and cut into squares or rectangles.
Notes
For a sweeter base, use graham cracker crumbs made from honey-flavored graham crackers.
Add a pinch of sea salt on top of the chocolate layer for a sweet-and-salty flavor twist.