Old-Fashioned Boiled Salad Dressing

1/2 cup granulated sugar
1 teaspoon salt
1 teaspoon dry mustard
1 tablespoon flour
1/2 cup milk
1 egg, beaten
1/2 cup cider vinegar
1/2 cup sour cream

In a saucepan, combine sugar, salt, mustard and flour. Add milk and beaten egg. In a separate pan, heat the vinegar and gradually add to the mixture. Cook over low heat until dressing has thickened. Cool slightly and mix with sour cream.