As promised, here's a recipe for the classic Béchamel Sauce. In England it's known as a "White Sauce".
According to the Larousse Gastronomique, the sauce is named after the "Marquis de Béchamel, Marquis de Nointel (1630–1703), a financier who held the honorary post of Chief Steward to Louis XIV. Béchamel is an improvement upon a similar, earlier sauce, the Tuscan "salsa colla", imported from Italy to France by Catherine de' Medici. It first appeared in "Le Cuisinier François", published in 1651 by François Pierre La Varenne (1615–1678), chef de cuisine to Nicolas Chalon du Blé, Marquis d'Uxelles.
The Escoffier method is considered to be definitive: make a white flour butter roux from equal parts of unsalted butter and flour, i.e. melt a big knob of unsalted butter in a hot small pan, and stir in an equal measure of flour. Next, gradually whisk in hot milk. As the flour cooks, it will form a smooth sauce. Season with sea salt, add an onion studded with a clove, and cook for eighteen minutes.