Boil the macaroni in salted water till just tender. Drain well.
Prepare a white sauce - melt the butter in a heavy saucepan, blend with the flour, and cook several minutes over medium heat. Heat the milk to the boiling point, stir into the flour-butter mixture, and continue stirring till it thickens. Add the seasonings and simmer 4 to 5 minutes.
Butter a 2 or 2-1/2 quart baking dish or casserole. In it arrange alternate layers of macaroni, sauce, and cheese, ending with cheese. Cover the top with buttered crumbs. Bake at 350°F 25 minutes, or until the top is nicely browned and the sauce is bubbly. Serve at once.