Line a 8x8 or 9x9 square baking pan with aluminum foil. Set aside.
In a medium bowl, mix the melted butter, graham cracker crumbs, and powdered sugar together until combined. Stir in ¾ cup of peanut butter. Spread into prepared baking pan.
In a small bowl, microwave 2 Tbs of peanut butter with the chocolate chips until melted. Stir until smooth. Spread over peanut butter layer.
Chill until completely firm, at least 3 hours. Allow to sit at room temperature for 10 minutes before cutting. Bars stay fresh stored in the refrigerator. Serve chilled. (Setting them out for a few hours at room temperature for serving is OK.) Bars may be frozen up to 2 months. Thaw overnight in the refrigerator.
*Unsalted butter may be used instead - add 1/4 teaspoon salt with the peanut butter in step 2.