Celery Sauce

A two-line assembly recipe that assumes you already know the base. The whole dish depends on the white sauce, so build that properly and the rest follows.

• What "medium white sauce" meansBy the standard ratios of the period, medium is 2 tablespoons butter and 2 tablespoons flour cooked together, then 1 cup milk whisked in and simmered until it coats a spoon. Thin is usually 1 tablespoon of each, thick 3 to 4; medium is the pouring consistency wanted here.
• Cook the roux outLet the butter and flour bubble a full minute or two before the milk goes in, or the sauce tastes of raw starch. Keep the heat moderate so the flour does not brown, which would tint the finished sauce.
• Cooking the celeryUse the tender inner ribs, cut small, and simmer in lightly salted water or chicken stock until soft, roughly 10 to 12 minutes. Drain well; wet celery thins the sauce and dilutes its flavour.
• Get more flavour from the trimmingsSimmer the celery leaves and coarse outer ribs in the milk, then strain before making the sauce. The original leaves the sauce plain; this is an optional way to deepen the flavour without extra ingredients.
• SeasoningThe recipe specifies none; salt, white pepper and a scrape of nutmeg suit a sauce of this kind. A spoonful of cream or a squeeze of lemon at the end lifts it if the sauce tastes flat.
• Texture choiceLeft as written the sauce is chunky. For a smooth version, purée it after the celery goes in and thin with a little milk or the celery cooking liquid.
• Yield and servingAbout 1 1/2 cups, enough for four servings with poached or boiled chicken. Serve hot, and if it stands, whisk it smooth over low heat rather than letting it boil hard.