In a heavy saucepan mix 1 cup sugar, 1/2 cup light corn syrup, 1 large can sweetened condensed milk and 1/8 teaspoon salt. Stir until sugar is well blended. Cook slowly, stirring gently, until a small amount of the mixture forms a soft ball when dropped in cold water (234 degrees F on a candy thermometer).
Remove from heat and stir in 1 teaspoon vanilla extract; cool slightly. Insert wooden skewer in stem end of each of 4 to 6 washed and dried red eating apples. Working quickly, dip apples in caramel and twirl until well coated. Coat with chopped nuts, if desired. Put apples, stem side up, on a buttered plate or wax paper to harden.
Makes 4 to 6.