Mix half a cupful of vinegar, one-fourth cupful of cold water, two eggs well-beaten, one tablespoonful of sugar, and three tablespoonfuls of butter, with salt and pepper to season. Cook until thick in a double boiler, stirring constantly; take from the fire, cool, and mix with a little cream. An entire cupful of cream may be used if desired. Mix with sliced boiled potatoes, seasoned with chopped onion and parsley.
The Myrtle Reed Cook Book, 1916