In a medium bowl, mix the butter, graham cracker crumbs, confectioners sugar, and 1 cup peanut butter until evenly blended.

Press evenly into the bottom of a 9x13 inch pan.

In a metal bowl over simmering water, or in the microwave (in a microwave safe container) melt the semi sweet chocolate chips, with the 4 tablespoons of peanut butter, stirring occasionally until smooth.

Spread over the prepared crust, and refrigerate for at least 1 hour until cutting into squares