As a young cook, I practiced Marcella Hazan's bechamel sauce for two days until I got it right—and I still use this creamy white sauce of butter, flour, and milk to luxuriously bind together my macaroni and cheese. With Hazan's lessons still in my head, I first cook the flour in the butter over low heat, taking care it doesn't brown (which yields a burned, pasty taste). I stir in hot milk a bit at a time, adding more only when the sauce thickens. Most important, I never stop stirring. Many recipes call for a wooden spoon, but I use a whisk, leaving little chance of lumps.