First, Boiled Icings is a generic term for a group of cake icings (aka frostings) that are “boiled”; more accurately, made usually from a hot sugar syrup, and / or cooked over a double boiler. Many were very economical, avoiding the use of eggs or fat (remember, dietary fat used to be expensive), and thus these icings tend to be either very low in fat, or fat-free. The thickening was achieved through the cooking instead. They were of an era when money was short, ingredients were luxuries, but there someone in the household had the extra time to cook a cake frosting.
Second, Boiled Icing is an icing in its own right. It is a smooth, glossy, fluffy frosting. A crust forms on the surface but the icing stays soft inside, with a consistency of melted marshmallow.
A sugar syrup is made, poured into beaten egg white, and the mixture beaten again. You need to apply it to the cake as soon as it is ready, because it will set quickly. It sets well, even on hot days.
Boiled Icing can also be used as a filling.
1 cup white sugar
1/3 cup water
1 tablespoon light corn syrup
1/8 teaspoon salt
2 egg whites
1 teaspoon vanilla extract
3 tablespoons icing sugar
In a large bowl, beat egg whites with a mixer until they are stiff, but still moist. Set aside.
Mix until well-blended in a saucepan the sugar, water, corn syrup, and salt. Bring to a slow boil without stirring until a little of the mixture dropped from a spoon back into the pot will form a long thread ( 238 – 242 degrees F / 114 – 117 degrees C). Note that the temperature on the sugar syrup will rise slowly at first, and then very fast, so don’t let it catch you out.
Drizzle the hot syrup slowly into the egg whites, beating all the while. Continue until mixture is fluffy and somewhat stiff. Add vanilla, and blend it in. If icing doesn’t seem as stiff as you want it, then beat the icing sugar a tablespoon at a time. Otherwise, leave it out. Spread on cake immediately.
Literature & Lore
“1. Cooked Frostings — (a) The so-called boiled frosting — a sugar and water syrup poured and beaten into stiffly beaten egg whites; the White Mountain frosting (the same but with a larger proportion of egg white); and the seven minute frosting, for which all ingredients are put together in the double boiler, and cooked under constant beating.” — Caldwell, Katherine. The National Cooking School Series: Lesson 10. St Petersburg, Florida: The Independent. Tuesday, 12 February 1935
“Boiled Icing: To one pound of the finest pulverized sugar, add three wineglasses of clear water. Let it stand until it dissolves. Then boil it until perfectly clear. Beat well the whites of four eggs. Pour the sugar into the dish with the eggs, but do not mix them until the syrup is lukewarm, then beat all together for one hour. Season to your taste with vanilla, rose water, or lemon juice. The first coating may be put on the cake as soon as it is well mixed. Rub the cake with a little flour before you apply the icing. While the first coating is drying continue to beat the remainder. You will not have to wait long if the cake is set in a warm place near the fire. This is considered an excellent recipe for icing.” — Charles H. Gibson. Mrs. Charles H. Gibson’s Maryland And Virginia Cook Book. John Murphy & Company. 1894