Line 8-inch square pan with foil, with ends of foil extending over sides of pan. Grease foil generously with shortening. Place grahams on bottom of pan, cutting to fit if necessary.
Microwave caramel bits and milk in microwaveable bowl on HIGH 2 min. or until caramel bits are completely melted and mixture is well blended, stirring every 30 sec. Pour over grahams; top with next 3 ingredients. Drizzle with chocolate.
Refrigerate at least 1 hour. Use foil handles to remove dessert from pan before cutting into bars to serve.