Melt the butter and peanut butter in a small sauce pan, remove from heat.
Mix peanut butter mixture with graham cracker crumbs and powdered sugar until completely blended. Press evenly into the bottom of an ungreased 9x13 inch pan.
In a metal bowl over simmering water, or in the microwave, melt the chocolate chips with 4 tbsp of peanut butter, stirring occasionally until smooth. Spread over the prepared crust. Refrigerate for at least one hour before cutting into squares.