For: boiled fish, boiled chicken, boiled lamb, boiled potatoes, asparagus, cauliflower, celery, broccoli
This quickly made and useful sauce does not belong to the béchamel and velouté family because it is made with an uncooked roux, or beurre manié. A golden color is given it by the addition of an egg yolk, and when flavored with enough butter it suggests a hollandaise.
Place the butter and flour in the saucepan and blend them into a smooth paste with a rubber scraper.
Pour on all the boiling liquid at once and blend vigorously with a wire whip.
Blend the egg yolk and cream with a wire whip, then, a few drops at a time, beat in ½ cup of sauce. Beat in the rest in a thin stream. Pour the mixture back into the saucepan. Bring to the boil over moderately high heat, beating, and boil 5 seconds. Remove from heat and season to taste with salt, pepper, and lemon juice. (*) If not used immediately, film surface with a half-tablespoon of melted butter.
Off heat, and just before serving, beat in the butter, a tablespoon at a time.