Meanwhile, melt 2 tablespoons butter in large saucepan over medium heat. Stir in flour and cook, stirring 1 minute. Gradually whisk in milk, mustard, salt and pepper. Bring to a boil, whisking. Boil 1 minute. Remove from heat and whip in cheeses until melted and smooth. Stir in drained macaroni.

Pour into shallow 2-quart baking dish. Melt remaining 2 tablespoons butter, stir in bread crumbs and sprinkle over macaroni. Bake at 375°F for 30 minutes. Let stand 10 minutes before serving.

Makes 8 servings.