1973 edition:
Melt in the top of a double boiler, over, not in, hot water: 3 ounces chocolate.
Combine, then stir into the chocolate: 1 well beaten egg, 3/4 cup evaporated milk, and 1 cup sugar.
Cook for about 20 minutes. Remove from heat and beat with a rotary beater for one minute or until well blended. Stir in: one teaspoon vanilla.
Cool sauce before using. If tightly covered and placed in refrigerator. will keep for several days.
