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Maple Frosting
1 cup maple sugar 1 egg white 1 cup boiling water teaspoon cream of tartar Boil sugar, water and cream of tartar until thread is formed. Pour on to the beaten white, and continue beating until of consistency to spread.
A boiled-syrup meringue frosting of the type that dominated American cake decorating before butter creams took over. The syrup temperature is the whole recipe.
- The hinge: syrup temperature"Until thread is formed" is usually given as roughly 230-235F on a candy thermometer, where a spoonful drops in a fine thread. At that stage the icing stays soft and can slump; many boiled-icing recipes take the syrup further, to about 238-240F (soft ball), for a frosting that sets firm enough to hold a swirl.
- A cup of water is a lotEqual volumes of sugar and water means a long boil to drive off the excess before the syrup even reaches thread. Nothing is wrong with it, but do not judge progress by time; judge by the thermometer or the thread test.
- Maple sugarHard cake or granulated maple sugar, sold by weight in New England and Canada. A cup of the granulated sugar weighs somewhere in the region of 5 to 7 oz depending on how finely it is ground. Maple syrup is not a direct substitute here because it brings its own water; if you use it, expect a much longer boil and a softer set.
- Cream of tartarThe quantity is lost in the original text; 1/4 teaspoon is a reasonable reading, though 1/8 is equally plausible. Its job is to invert some of the sucrose so the icing does not turn grainy, and a small excess does no harm.
- Pouring on the whiteBeat the white to soft peaks first, then add the syrup in a thin steady stream down the side of the bowl while beating. Poured all at once it scrambles the white and sets into lumps.
- Beating timeTen to twelve minutes with a stand mixer, considerably longer by hand, until the bowl is barely warm and the mass holds its shape. Stop while it still spreads; beaten past that point it turns to fudge in the bowl.
- WeatherBoiled icings are hygroscopic and stay tacky on a humid day. Make it on a dry day, or push the syrup to the upper end of the temperature range.
- YieldA small batch: enough to cover the top and sides of one 8- or 9-inch layer, and thin for filling and covering two. It is best used the day it is made; refrigeration makes it weep.
Lowney's, a Boston chocolate house, published its cook book to sell cocoa, but the dessert chapters take in the whole New England sweet repertoire, and maple sugar was still a cheap regional staple when this was written - sold in cakes at the grocer and grated or broken up for baking. Boiled frosting of this kind, syrup poured onto beaten egg white, spread as an American cake icing over the later nineteenth century; it depended on nothing more than sugar, an egg and patience, and it long predates the powdered-sugar-and-butter frostings that displaced it once confectioners' sugar became cheap and reliable. The technique is the same one used for Italian meringue and for divinity, and the thread and soft-ball stages are often said to have been judged by eye and finger rather than by thermometer.