Cook macaroni just until tender according to package directions. Drain and set aside.
Melt 1/2 cup butter in a heavy saucepan over low heat; whisk in flour until smooth. Cook 1 minute, whisking constantly. Gradually whisk in milk; cook over medium heat, whisking constantly, until mixture is thickened and bubbly. Add cheese and next 3 ingredients; stir until cheese melts. Stir in macaroni.
Spoon macaroni and cheese into a greased 13" x 9" baking dish or other large baking dish. (Dish will be very full.) Toss breadcrumbs with 6 tablespoons melted butter until crumbs are well coated. Sprinkle over macaroni.
Bake, uncovered, at 350° for 30 minutes or until thoroughly heated and top is golden.
Note: Make fresh breadcrumbs easily by tearing a few pieces from a French baguette. Pulse bread in a food processor or mini chopper until you get coarse crumbs.