How to Make It
Melt the butter in a large saucepan. Whisk in the flour and cook over moderately high heat, whisking constantly, until golden brown, 2 to 3 minutes. Slowly whisk in the milk and cook over moderate heat, whisking frequently, until the sauce is thickened, about 15 minutes. Remove the sauce from the heat and season with salt, pepper and the nutmeg. Use at once.