chocolate peanut butter bars

in a medium bowl, mix together the butter, graham cracker crumbs, confectioners' sugar, and the 1 cup of peanut butter until well blended. then press evenly into the bottom of an ungreased 9x13 inch pan. in a metal bowl over simmering water, melt the chocolate chips with the 4 tablespoons of peanut butter, stirring occasionally until smooth. then spread over the prepared crust. refrigerate for at least an hour before cutting into squares.