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Boiled Frosting, Splendid
Pour one-half pint boiling water over three cups pulverized or granulated sugar, and boil until a spoonful placed on a cold plate will stir to a thick cream. Pour this over the whites of four eggs beaten to a stiff froth, and stir until cold and creamy; add onehalf teaspoon of tartaric acid. Flavor to taste and spread on the cakes.
This is a classic Italian-meringue frosting: hot sugar syrup whipped into beaten whites. The whole thing hangs on getting the syrup to the right stage, and the old plate test is workable but a thermometer is surer.
- The syrup is the hinge"stir to a thick cream" on a cold plate corresponds roughly to what we would call the soft-ball stage, somewhere in the region of 238-240F on a candy thermometer. Under-boiled syrup gives a frosting that never sets and runs off the cake; over-boiled syrup sets hard and sugary before you can spread it.
- Half a pintOne cup of boiling water to three cups sugar. Use a heavy saucepan with room to spare, since the syrup climbs as it boils.
- Pulverized sugarIn this period "pulverized" meant granulated sugar ground fine, not modern confectioners' sugar, which contains cornstarch. Plain granulated is the right substitute and is what the recipe offers as the alternative anyway.
- Tartaric acidSold by the ounce at druggists then, less common now. Half a teaspoon of tartaric acid is roughly equivalent in acid strength to about a teaspoon of cream of tartar, which is easier to buy; acid in a boiling sugar syrup inverts some of the sugar and helps keep the frosting from turning grainy. Note that this recipe adds the acid at the end, once the mixture is cold, rather than to the boiling syrup.
- Pouring and beatingAdd the syrup to the whites in a thin steady stream at the edge of the bowl, not into the beaters, or it will spin into hard threads. With a stand mixer expect eight to twelve minutes of beating on medium-high before the bowl feels cool to the hand.
- FlavoringA teaspoon of vanilla, or a teaspoon of lemon juice with a little zest, added once the mixture has cooled. Some of an alcohol-based extract's flavour is likely to be lost if it goes in while the mass is still hot.
- EggsThe 240F syrup brings the whites well up in temperature but does not reliably hold them there. If you are serving anyone who should avoid undercooked egg, use pasteurized whites.
- Yield and keepingEnough to fill and cover a two-layer nine-inch cake generously. Spread it the day it is made; it crusts on the outside within hours and weeps if refrigerated.
Boiled frosting is often associated with the last third of the nineteenth century, when cheap refined white sugar, reliable eggbeaters and the fashion for pale layer cakes were all features of American kitchens, though the technique appears in American and European cookery well before that. Cooks distinguished it from plain "water icing" or uncooked confectioners' frosting by the boiling, which gave a glossy, marshmallowy coat that held its shape on a cake's sides -- the same principle a pastry cook now calls Italian meringue. The tartaric acid can generally be read as a period marker: household manuals of the era commonly sent readers to the druggist for tartaric acid, cream of tartar and saleratus, and acid was widely understood to keep boiled sugar from crystallizing back into grit. The confident subtitle "Splendid" is also said to be typical of community and household cookbooks of the day, where recipes tended to compete for attention by testimonial rather than description.