Beat margarine and sugar until light and fluffy. Add flour; mix well. Press onto bottom of 8-inch square baking pan. Bake at 350 degrees for 15 minutes or until lightly browned. Combine Marshmallow Creme and peanut butter, mixing at medium speed on mixer until well blended. Carefully spread over crust. Melt chocolate and shortening in small saucepan over low heat. Spread over Marshmallow Creme mixture. Sprinkle with peanuts. Chill. Cut in bars. Makes 20 bars.