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Cocoa Filling for Cake
Left-over cocoa can easily be made into a filling for cake by adding two tablespoonfuls of dissolved arrowroot to one cup of cocoa, reheating to the boiling-point, adding more sugar if necessary, the yolk of one egg, slightly beaten, and a little salt. Remove from the fire as soon as the egg is added.
When nearly cool add one-half teaspoonful of vanilla and spread between the layers.
A thrift filling built on yesterday's cup of drinking cocoa, thickened with arrowroot and enriched with a yolk. The hinge is the egg: it goes in off the heat and must not be allowed to boil, or the filling curdles and turns grainy.
- What "cocoa" means hereNot cocoa powder but leftover drinking cocoa — powder cooked with sugar and milk or water. If you are starting from scratch, make one cup of unsweetened drinking cocoa on the strong side, since it will be diluted slightly by the arrowroot slurry.
- The arrowroot measurement is ambiguous"Two tablespoonfuls of dissolved arrowroot" could mean two tablespoons of dry starch slaked in cold liquid, or two tablespoons of the finished slurry. For one cup of liquid, about 1 tablespoon of dry arrowroot stirred smooth in 2 tablespoons cold water gives a spreadable filling; two full tablespoons of dry starch sets it close to a sliceable pudding.
- Arrowroot behaves unlike flourIt thickens at just below boiling and thins again if held at a hard boil or overstirred. Bring the cocoa to the boiling point, add the slurry, and pull it off as soon as it turns glossy and coats the spoon.
- Temper the yolkBeat the yolk with a spoonful of the hot cocoa before stirring it into the pan, then return the pan to the heat for no more than a few seconds. A cold yolk dropped straight into a near-boiling pan is the likeliest route to a curdled, grainy filling.
- Sugar and saltNo quantity is given because the leftover cocoa was already sweetened. Taste after thickening; a filling that will sit against plain cake usually wants to read slightly too sweet on the spoon. The salt is a pinch, and it matters more than it sounds — it sharpens thin cocoa considerably.
- CoolingAdd the vanilla only when the mixture is nearly cool, as the recipe directs; volatile flavour is carried off in steam from a hot pan. Lay plastic wrap or buttered paper directly on the surface while it cools to stop a skin forming.
- Yield and keepingAbout one cup, enough between the two layers of an 8- or 9-inch cake, or three thin layers spread sparingly. It contains egg, and milk too if the cocoa was made with it, so the filled cake keeps in the refrigerator and is best eaten within two days.
The Cook Book of Left Overs belongs to a long line of American and English household manuals whose argument was moral as much as culinary: a well-run kitchen wasted nothing, and the cook who could turn yesterday's breakfast cocoa into today's cake filling was a better manager than one who poured it out. Arrowroot, milled from the rhizome of Maranta arundinacea and imported chiefly from the West Indies, was a favoured thickener of the invalid tray and the nursery in this period — valued because it set clear and was thought lighter on the stomach than wheat flour or cornstarch. Cocoa itself became an everyday drink after nineteenth-century pressing and alkalizing methods made the powder cheaper and easier to mix, and a jug of it left from breakfast would have been a plausible surplus in a house with children.