Cook macaroni according to package directions. Melt butter in saucepan and blend in flour with whisk. Cook for a minute. Add milk and stir until sauce thickens. Add grated cheese, onion and mustard to sauce mixture and fold in mayonnaise. Combine noodles, broccoli, ham and sauce, season with salt and pepper. Pour into greased 2 quart casserole and top with buttered bread crumbs. Bake at 375 for 25-30 minutes.