In a medium bowl, mix together melted butter, graham cracker crumbs, powdered sugar, and peanut butter until well combined.
Press the mixture into the bottom of a 9x13-inch baking dish.
Melt the chocolate chips and 4 tablespoons of peanut butter in a microwave-safe bowl in 30-second intervals, stirring after each, until smooth.
Spread the melted chocolate mixture over the peanut butter layer in the dish.
Refrigerate for at least 2 hours or until set.
Cut into bars and serve.