LINE 8-inch square pan with foil, with ends of foil extending over sides. Beat butter and peanut butter with mixer until blended. Add wafer crumbs; mix well. Gradually beat in sugar. Press onto bottom of pan.
MICROWAVE COOL WHIP and chocolate in microwaveable bowl on HIGH 1 min.; stir. Microwave 15 to 30 sec. or until chocolate is melted; stir until well blended. Spread over peanut butter layer.
REFRIGERATE 2 hours. Use foil handles to lift dessert from pan before cutting to serve.