Maple Frosting
1/8 cup maple sugar. 1/2 cup boiling water.
White 1 egg. 1 teaspoon cream of tartar.
PROCESS: Boil sugar, water and cream of tartar together until it spins a thread from tip of spoon. Pour slowly in a fine stream on the beaten white and continue beating until of the consistency to spread over cake. (To get the exact proportion of sugar, weigh one level cup of granulated sugar to ascertain by weight how much Maple sugar is required for this amount of water and white of one egg. It will weigh about one-half pound.)
This is an Italian meringue by another name: hot syrup beaten into egg white until it sets soft. Two things decide whether it works — the temperature of the syrup and the steadiness of the pour.
- Thread stage means 230-235FThe syrup spins a thread from the spoon at about 230-235F on a candy thermometer. Below that the frosting stays runny; much above it and you get a hard, brittle coat that cracks when the cake is cut.
- Weigh the maple sugarThe parenthetical instruction is the useful part of the recipe. Maple sugar came in pressed cakes of varying density, so a cup was unreliable; use 8 oz (about 1/2 lb) by weight against the 1/2 cup water. If your maple sugar is a hard cake rather than granules, grate or break it small so it dissolves before the syrup comes to a boil.
- Cream of tartar's jobIt inverts a little of the sugar and keeps the syrup from crystallising into a grainy mess. Do not skip it, and do not stir the syrup once it boils or scrape the pan sides into the bowl.
- Beat the white firstHave the white at soft peaks before the syrup is ready, not after. A stand mixer makes the pour manageable; by hand this is genuinely a two-person job, one pouring in a fine stream down the side of the bowl, one beating.
- Keep beating until coolThe frosting is ready when the bowl is no longer warm to the touch and the meringue holds a soft peak — usually 5 to 8 minutes of beating after the syrup goes in. Spread it at once; it firms as it sits and skins over within an hour.
- Humidity mattersBoiled frostings weep and refuse to set on a damp day. Cook the syrup two or three degrees higher if the kitchen is humid.
- YieldOne white and a half pound of sugar gives roughly two cups of frosting -- enough to cover a single 8- or 9-inch layer cake thinly, or to top a sheet cake.
- On the egg whiteThe hot syrup raises the temperature of the white but does not hold it there long enough to pasteurise it, so treat the frosting as containing lightly cooked egg. If you are serving someone pregnant, elderly or immune-compromised, use pasteurised egg white.
52 Sunday Dinners arranges its menus week by week through the year, and maple appears where the domestic calendar put it: sugar made in the late-winter runs of the New England and Great Lakes maple bush, then kept in hard cakes on the pantry shelf for the rest of the year. Before cane sugar became cheap and universal, maple sugar was the ordinary sweetener across much of the northern United States and eastern Canada, and it was often sold pressed into moulds, though granulated forms were also common — hence the recipe's careful instruction to weigh it against a known cup of white sugar rather than trust a measuring cup. The method itself is the boiled or "white mountain" icing, a household version of the Italian meringue, widely found in American cake books of the period.