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Maple-Sugar Frosting
1/2 pound maple sugar Whites of 2 eggs 1/2 cup milk Scrape the sugar into a saucepan; add the milk and stir over the fire until it spins a thread. Pour hot over the beaten whites of eggs; beat until it begins to thicken and spread quickly between the layers of cake.
A boiled maple meringue frosting, essentially an Italian meringue made with maple sugar and milk instead of sugar and water. The whole thing hinges on the syrup stage and on working fast once it thickens.
- Thread stage means 230-234F"Spins a thread" is the old test for syrup that trails a fine thread from a lifted spoon, about 230-234F on a candy thermometer. Below that the frosting will not set; much above it and you are heading toward fudge.
- Maple sugarThis is solid cake maple sugar, sold in blocks and grated or scraped down, not maple syrup and not maple-flavoured granulated sugar. Half a pound is 8 oz by weight, which will measure somewhere around a cup to a cup and a quarter depending on how coarsely it is scraped; if you substitute pure maple syrup you must cook off the extra water, which changes the timing considerably.
- Milk in the syrupThe milk makes this closer to a maple cream than a plain meringue and it will scorch readily. Use a heavy saucepan, stir steadily, and keep the heat moderate rather than high.
- Beat the whites firstThe recipe assumes the two whites are already beaten before the syrup is ready, so have them whipped and waiting. It directs you simply to pour the hot syrup over them and then beat until it thickens; modern practice would add the syrup in a thin steady stream with the beater running.
- Raw egg riskSyrup at thread stage does not bring the whites to a pasteurising temperature the way a 240F soft-ball syrup comes closer to doing. Pasteurised egg whites are the sensible choice if the cake is for children, elderly guests, or anyone pregnant or immune-compromised.
- Spread quickly is not a flourishMaple sugar grains readily, and this frosting can stiffen and turn coarse in the bowl. Have the cake layers cooled and waiting before you start the syrup.
- YieldHalf a pound of sugar with two whites makes enough to fill between the layers as the recipe directs; if you also want to cover the top and sides you will need more.
Maple sugar, not maple syrup, was the household form of the sweetener across the northern United States and Canada well into the twentieth century: sap was boiled down past the syrup stage and poured into moulds, giving hard cakes that kept without refrigeration and travelled well. Cooks scraped or grated what they needed, which is exactly what this recipe assumes. In sugaring districts it was often the cheaper sweetener, and cookbooks of the period treat it as a straight substitute for refined sugar in candies, fillings and frostings. The technique here, hot syrup beaten into egg whites, is the same one behind boiled white icing and what later cooks call Italian meringue.