Allemande Sauce with Mushroom Essence

After the veloute (No. 415) sauce is reduced in a flat saucepan with a fifth part of mushroom essence (No. 392), thicken with twelve egg-yolks, some nutmeg and two ounces of butter, incorporate slowly a part of the sauce into the thickening, then pour the whole into the sauce, adding the juice of one lemon. Set the saucepan on the fire, stir at the bottom with a spatula, boil the sauce for one minute, then strain through a tammy; pour it in a high saucepan and set it in a bain-marie, and cover it with a little white stock (No. 422) to prevent the surface from drying or set it away in a vessel for further use.