Cream Sauce with Mushrooms

A one-line instruction that assumes you already know the base sauce. Everything depends on what the book means by "cream sauce" and on how you treat the mushrooms.

• The cream sauce, in period termsA cream sauce of this era is typically 2 tablespoons butter and 2 tablespoons flour cooked together without browning, then 1 cup of milk or thin cream whisked in and simmered until it coats a spoon. Season with salt and pepper; a scrape of nutmeg is optional.
• Cook the mushrooms firstRaw chopped mushrooms are roughly 90 percent water, and ten minutes in the sauce will thin it and turn it grey. Sauté them in butter over fairly high heat until the liquid they give off has evaporated, then stir them in.
• Ten minutes is for flavour, not safetyOnce the mushrooms are cooked, the ten minutes simply lets their flavour move into the sauce. Keep it at a bare simmer and stir, or the flour will catch on the bottom of the pan.
• "Fresh mushrooms"In American kitchens of this period this most likely meant the cultivated Agaricus sold by grocers, then usually a cream or brownish strain rather than today's white button. Cremini or a handful of dried porcini soaked and chopped will give considerably more flavour.
• Chop coarsely if you likeSliced mushrooms give a better texture in the finished sauce and nothing in the method objects.
• Yield and useOne cup of milk plus a cup of mushrooms makes enough sauce for four servings over toast, chicken, veal, poached eggs or boiled vegetables. Thin it with a little more milk if it stiffens on standing.