Preheat oven to 350°F.

Melt butter in saucepan over moderate heat, blend in flour and mustard, slowly stir in milk, and cook, stirring until thickened. Mix in 2 cups grated cheese and all remaining ingredients except macaroni. Taste for salt and add a little more if needed. Cook and stir until cheese melts.

Off heat, mix in macaroni; turn into a buttered 2-quart casserole, sprinkle with remaining cheese, and bake, uncovered, about ½ hour until bubbly and lightly browned.