Coffee Sauce

A thin pouring sauce for steamed and baked puddings, thickened with a little cornstarch and enriched with one egg. The whole thing takes under ten minutes, and most of the ways it goes wrong happen in the last thirty seconds.

• Slurry the cornstarch firstBeat the egg and cornstarch together with a few spoonfuls of cold coffee before the hot liquid goes in. Dry starch dropped into a beaten egg and then hit with boiling syrup will seize into knots, which is why the original tells you to strain.
• Finish it over heatCornstarch does not reach full thickening power until the mixture comes back to a simmer, and a sauce built entirely off-heat may stay thin and taste of raw starch. Return the strained mixture to the pan and cook it gently, stirring, until it just bubbles; that also carries the single egg well past 160F.
• Strong coffeeIn a book of this era this most likely means drip or boiled coffee brewed noticeably stronger than usual, not espresso. Roughly twice the usual quantity of grounds is a reasonable reading, though the recipe itself gives no guidance.
• Yellow corn syrupMost likely the light amber sort rather than the crystal-white grade; modern light corn syrup is the nearest substitute. Golden syrup will also work, though it is sweeter and more caramelly.
• Boil the coffee and syrup brieflyA minute or two of hard boiling is enough to combine them and drive off a little water. Long boiling concentrates the coffee's bitter compounds and the sauce turns harsh.
• Strain while hotPass it through a fine sieve immediately, before any set threads of egg firm up. Waiting until it cools makes the job much harder and costs you sauce.
• Cooling and consistencyIt thickens noticeably as it cools, to about the body of thin cream. If it sets too stiff in the refrigerator, slacken it with a spoonful of hot coffee or milk.
• Yield and servingMakes roughly 2 1/2 cups, enough for about eight servings. Intended cold or barely warm over cottage pudding, steamed suet or bread puddings.