BEAT butter and 3/4 cup peanut butter in large bowl with mixer until well blended. Add graham crumbs; mix well. Gradually beat in 2 cups sugar; press onto bottom of 9-inch square pan sprayed with cooking spray.
BEAT cream cheese, remaining peanut butter and remaining sugar with mixer until well blended. Spread over crust.
MICROWAVE COOL WHIP and chocolate in microwaveable bowl on HIGH 2 to 2-1/2 min. or until chocolate is completely melted and mixture is well blended, stirring every minute. Spread over cream cheese layer. Refrigerate 2 hours.