Cheese Sauce

A cornstarch-thickened cheese sauce of the sort kept on hand for scalloped oysters, baked clams and shellfish gratins. The whole thing hinges on heat control at the end.

• Never let it boil after the eggOnce the milk and egg are in, hold the pan at a bare steam, around 170-180F. Boiling will curdle the egg and split the cheese into grains and oil.
• The unusual orderButter and cornstarch go together first, then the cheese and seasonings, then the hot milk. Cheese into a dry paste is stiff work; keep the heat low and moderate, and add the hot milk in a thin stream while stirring so no lumps set.
• Cornstarch, not flourTwo tablespoons of cornstarch to a cup and a half of milk gives a thick, coating sauce. Cornstarch thickens fully only as it nears a simmer, which is one reason the milk goes in already hot; note that the recipe itself forbids boiling once the milk and egg are added.
• Temper the eggBeat the egg in a cup, stir in a few spoonfuls of the hot sauce, then return the mixture to the pan off the heat. Dropping a whole egg into a hot pan invites strands of cooked white.
• The cheeseA period recipe of this kind assumes a firm, dry, sharp cheese: aged Cheddar or a hard American cheese. Grate it yourself; bagged shreds carry anti-caking starch that fights the cornstarch and makes the sauce grainy.
• Red pepper and paprika"A dash of red pepper" means cayenne, perhaps an eighth of a teaspoon. The paprika is most likely a mild, sweet type used largely for colour, in which case it will not stand in for the cayenne.
• YieldAbout two cups, enough to sauce oysters or clams for four to six as a gratin, or to nap a pound of pasta or a head of cauliflower.
• Holding and reheatingIt thickens and skins as it cools. Keep it in a covered pan over hot, not boiling, water and thin with a little warm milk when serving.