Scald the milk in a double boiler. Mix the cocoa, sugar, and salt. Stir the boiling water into this mixture gradually, and let it boil for several minutes over the fire. Then turn the mixture into the hot milk in the double boiler, and beat all with an egg beater for several minutes. A drop of vanilla added to the cocoa just before serving adds to its flavor.
Woman's Institute Library of Cookery, Volume 1.