Cocoanut Filling

A four-ingredient boiled custard filling for layer cake, of the kind that turns up in nearly every American cookbook of the period. The whole difficulty is in the eggs.

• Cook it gently, not fastTwo eggs in one cup of milk can scramble over direct heat inside five minutes. Use a double boiler, or a heavy saucepan over low heat, and stir constantly until the mixture coats the back of a spoon at about 170-175F.
• "Cocoanut" means fresh coconut"Cocoanut" means grated coconut meat -- The older spelling is simply the older spelling. The recipe most likely means freshly grated coconut, which carries its own moisture and fat, though prepared desiccated coconut was also on sale by this date. Unsweetened desiccated or frozen grated coconut works; if you use sweetened flaked coconut, cut the sugar to about half a cup.
• Whole eggs, beaten firstBeat the eggs and temper them with a little of the warm milk before combining, or the whites will set in threads before the custard thickens.
• It thickens on coolingFive minutes gives a loose custard that looks too thin to spread. Cool it fully, covered, before it goes near the cake; it will set to a spreadable consistency and stiffen further in the refrigerator.
• If it needs helpFresh coconut varies a good deal in moisture, and a thin batch is common. A scant teaspoon of cornstarch whisked into the sugar before heating gives insurance without changing the flavour.
• YieldUpwards of two cups, enough to fill between two 8- or 9-inch layers. It is a filling rather than an icing and will not hold up on the sides of a cake.
• KeepingAn egg-and-milk custard with no acid or alcohol is perishable. Refrigerate the filled cake and eat it within two days.