HEAT oven to 350ºF.
LINE 13x9-inch pan with foil, with ends of foil extending over sides. Cook caramels and milk in saucepan on low heat 10 to 15 min. or until sauce is smooth, stirring frequently. Remove from heat.
MIX next 5 ingredients in large bowl. Cut in butter with pastry blender or 2 knives until mixture resembles coarse crumbs; press 3 cups onto bottom of prepared pan. Bake 10 min. Spread chocolate over crust; top with nuts, caramel sauce and remaining crumb mixture.
BAKE 25 min. or until golden brown. Cool completely. Use foil handles to lift dessert from pan before cutting into bars. Refrigerate 3 hours or until chilled.