Melt the butter in a heavy saucepan, stir in the flour with a wooden spoon, and cook for less than a minute over a tiny flame before beginning to add the milk, very slowly at first, stirring rapidly the while to prevent lumping (should lumps form, it is no disaster: Finish adding the milk, bring it to a boil, strain it, whisk, and put it back to cook). After further additions of milk, turn the flame up a bit. Stir constantly, adding more milk only as the previous addition begins to thicken (remove the saucepan from the heat for a moment if thickening too rapidly). The last half may be poured in steadily while stirring. Bring to a boil and adjust the heat, using an asbestos pad, if necessary, to keep the sauce at the slightest suggestion of a boil. Undersalt—seasoning may always be rectified. Stir from time to time, thoroughly scraping sides and bottom, the sauce tending to settle and thicken there. After long cooking, this repeated scraping will make the sauce rather uneven, but that is unimportant for a gratin, and if you are using the sauce as a base for others, simply whisk it or strain and whisk it again. Nutmeg is sometimes added (it should be used so sparingly as to be nearly undetectable) and cream—as much as one likes—may be used to thin and to enrich the sauce.
Copyright © 1974 by Richard Olney. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.