Cook caramels and 1/3 cup milk in saucepan on low heat 5 to 7 min. or until caramels are completely melted and mixture is well blended, stirring frequently.
Remove from heat.
Combine cake mix, butter and remaining milk; press half onto bottom of 13x9-inch pan sprayed with cooking spray.
Bake 10 min.
Sprinkle with 1 cup nuts and 1/2 cup chopped chocolate.
Drizzle with caramel sauce; carefully spread to edges of pan. Top with teaspoonfuls of the remaining cake mix mixture; press gently into caramel sauce with back of spoon.
Sprinkle with remaining nuts and chocolate.
Bake 18 min. or until lightly browned. Cool completely before cutting into bars.
