Yellow Sauce

A stirred custard sauce thickened with both egg and cornstarch, meant to be poured hot over a pudding or steamed dessert. The instruction "cook as a custard" assumes the reader already knows the technique, which is where the whole recipe lives.

• The hinge: heat controlWhisk the sugar, cornstarch and yolks together, temper in the scalded milk, then cook over low heat or a double boiler, stirring constantly, until it coats a spoon. Because cornstarch is present the sauce can be brought to a bare simmer for a minute to cook out the starchy taste, but hold it there and no further or the yolks will curdle into grains.
• "Sweet milk"Simply fresh unsoured whole milk, distinguished in period books from buttermilk or sour milk. Use whole milk; skim gives a thin, chalky sauce.
• When to add the butterStir it in off the heat at the end; whisked in last it gives the sauce gloss and a rounder mouthfeel.
• Flavoring with orangeThe recipe specifies only "orange," which could be an extract, orange-flower water, or the zest. Grated zest steeped in the hot milk and strained out works better than juice, which is acidic enough to thin the custard and can make it separate.
• SweetnessA cup of sugar to two cups of milk is very sweet by current taste, which would suit a plain steamed or boiled pudding beneath it. Two-thirds of a cup is closer to modern palates if the dessert is already sweet.
• StrainingPour through a fine sieve as soon as it comes off the heat. This catches the inevitable few set flecks of egg and any skin, and costs nothing.
• Yield and holdingAbout two and a half cups, enough for six to eight servings. It thickens noticeably as it cools; keep it warm over hot water with a round of parchment on the surface, and thin with a little hot milk if it stiffens.