In a medium bowl, mix together the butter or margarine, confectioners' sugar, and 1 cup peanut butter until well blended. (hint if it isn’t thick enough add more powdered suger) 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 the 4 tablespoons peanut butter, stirring occasionally until smooth. Spread over the prepared crust. Refrigerate for at least one hour before cutting into squares.