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Marshmallow Frosting
1 cup sugar cup hot water pound marshmallow white of one egg 1 teaspoon vanilla Melt marshmallows in double boiler. Cook sugar and water until thread is formed. Pour on to the beaten white. Add melted marshmallows, flavoring, and beat until of consistency to spread.
This is an Italian-style meringue frosting stretched with melted marshmallow, and the transcription has lost two fractions along the way. Read the syrup stage carefully; everything else follows from it.
- The missing quantitiesThe water and marshmallow amounts have dropped their fractions in the original printing, so neither can be recovered with certainty. Comparable frostings of the period use about 1/4 cup water to a cup of sugar, and a quarter to a half pound of marshmallows; treat those as informed guesses rather than the author's figures.
- "Until thread is formed"Thread stage is roughly 230-235F on a candy thermometer, when a spoonful drizzled from the pan spins a thin filament rather than dropping in beads. Boiled much beyond that, the syrup gives a stiffer frosting that sets faster and is harder to spread.
- Pouring the syrupAdd it to the already-beaten white in a slow steady stream down the side of the bowl while beating continuously. Dumped in at once it scrambles the white and leaves cooked flecks through the frosting.
- Marshmallows have changedCommercial marshmallows of this period were generally denser and less aerated than the modern kind. Modern bagged marshmallows are mostly air, so a half pound is a large volume; melt them in the double boiler with a tablespoon or two of water to keep them fluid enough to fold in.
- Working temperatureThe melted marshmallow must go in while the meringue is still warm. Once the mixture cools it stiffens quickly, and further beating makes it tear rather than smooth out.
- Egg whiteSyrup at thread stage warms the white but does not reliably bring it to a pasteurizing temperature. If the frosting is for someone elderly, pregnant or immune-compromised, use pasteurized whites.
- YieldRoughly enough to fill and cover a two-layer 8- or 9-inch cake, or a dozen or so cupcakes. Best spread the day it is made; it crusts on the surface and can weep if held.
Lowney's Cook Book was compiled by Maria Willett Howard and published in 1907 for the Walter M. Lowney Company, a Boston chocolate manufacturer, and like other maker-sponsored cookbooks of its era it leans heavily on confectionery and dessert work. Marshmallow took its name from the marsh mallow plant, whose root mucilage was the original whipping agent, but by the later nineteenth century American manufacturers had largely shifted to gelatin and marshmallows were sold ready-made by the pound -- which is why a household recipe of this date can call for melting them down as an ingredient rather than making them. The technique here, hot sugar syrup beaten into egg white, is the boiled icing that was widespread in American cake work before butter-based frostings took over, and the marshmallow would help stabilize it against the weeping and cracking plain boiled icing was prone to.