Preheat oven to 325 degrees. Sprinkle nuts into pie shell. In small saucepan, over low heat, melt caramels with 2/3 cup sweetened condensed milk. Spoon over walnuts. In mixing bowl, combine egg, margarine and remaining milk; mix well. Stir in chips. Pour chocolate mixture over caramel layer. Bake 35 minutes or until center is set. Cool. Serve warm or chilled. Refrigerate leftovers. Whipped topping is optional.