LINE 8-inch square pan with foil, with ends of foil extending over sides. Beat butter and peanut butter with mixer until blended. Mix in wafer crumbs. Gradually add sugar, mixing well after each addition. 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 blended. Spread over peanut butter layer.

REFRIGERATE 2 hours. Use foil handles to lift dessert from pan before cutting to serve.