Rub together 1 tablespoon of flour and 1 of butter, and put in a saucepan; as it melts add slowly 1 cup of boiling water or vegetable stock, let boil, stirring constantly, then remove from the fire, and when somewhat cooled add the juice of 1 lemon, 2 tablespoons of tarragon or chervil vinegar, 2 egg-yolks slightly beaten, and salt and pepper.
GERMAN SAUCE
Make brown sauce, add ½ can halved button mushrooms and 1 tablespoon of reduced vinegar, and season with salt and pepper.
GERMAN EGG SAUCE
Mix 3 beaten egg-yolks with 1 teaspoon of flour, 1 scant cup of cream or milk, 1 tablespoon of butter, and 1 tablespoon of lemon juice, season with salt and pepper, and beat vigorously, until thickened, over a hot fire, but do not let the sauce boil at all. Add 1 hard-boiled egg, chopped fine, and 1 tablespoon of minced parsley before serving.
HERB SAUCES
Make a good white sauce and to each 2 cups of sauce add the herbs selected, prepared as follows: Take a handful of the leaves, and after washing them well put them in a pan with a little salted boiling water; let cook for five minutes, then drain, and dry with a cloth, and put in a mortar with 1 tablespoon of butter, and macerate until fine; add this to the white sauce. In this way parsley, mint, tarragon, chervil, and other herb sauces can be made.