Boiled Frosting
1 cup granulated sugar 1/3 cup cold water Let boil until long thread forms. Pour syrup slowly on the stiffly beaten white of egg. Beat until ready to spread. 2 tbsp. cocoa may be added.
— Mrs. F. H. Sellars
This is an Italian meringue under an older name: hot sugar syrup beaten into egg white until it holds a spreadable gloss. The recipe assumes you know how many whites to use and how to read a syrup by eye, so those are the two gaps worth filling.
- Egg countThe original says "the stiffly beaten white of egg," singular. One large white to 1 cup sugar is the standard proportion for this style of frosting and gives a firm, marshmallowy icing; two whites yields a lighter, fluffier one that spreads further.
- "Until long thread forms"Thread stage on a candy thermometer is roughly 230-235F, when syrup lifted on a spoon trails a fine thread. Many modern versions of this frosting take the syrup a little further, to 238-240F (soft-ball), for an icing that sets rather than weeps. Do not stir once it boils, and wash any crystals off the pan sides with a wet brush.
- Pour slowly means slowlyA thin steady stream down the inside of the bowl, with the mixer running, is the hinge of the whole recipe. Dumped in at once, the syrup cooks the white into threads and the frosting turns grainy and thin.
- Beat until ready to spreadRoughly seven to twelve minutes in a stand mixer, until the bowl is no more than warm to the touch and the meringue holds a peak that just bends at the tip. Frosting spread while still hot will slide off the cake.
- CocoaThe 2 tablespoons of cocoa should be sifted in near the end of beating, once the mixture has cooled and thickened; added earlier it clumps. Cocoa sold for home baking in this period was usually natural rather than Dutch-process, and so slightly more acidic, which does no harm here.
- HumidityBoiled frosting is sugar held in suspension and it draws water from the air. On a damp day it may refuse to stiffen; a pinch of cream of tartar or 1/2 teaspoon corn syrup in the sugar syrup makes it more forgiving.
- YieldEnough to frost the top and sides of an 8- or 9-inch cake, or to top a sheet cake. Use it the day it is made, as it crusts on the surface and dries out by the second day.
Boiled frosting, also sold under the name white mountain icing, became a household staple around the time cheap refined granulated sugar and reliable eggbeaters came within reach of ordinary kitchens, generally traced to the later nineteenth century. Earlier cakes were often iced with a raw royal icing of egg white beaten with powdered loaf sugar, which set brittle and hard; the boiled method gives a soft, glossy coating that stays sliceable. The cocoa variation at the end reflects how quickly cocoa powder moved into home baking after commercial tins became common. Its appearance here, credited to a named contributor, is typical of church and society cookbooks like the Philathea, which were compiled from members' own working recipes and printed with the abbreviations and assumed knowledge of a cook writing for her neighbors rather than for strangers.