PREPARATION:
Cook beans; drain and reserve 1/2 cup of cooking liquid (Heat through if using canned beans). Melt 2 tablespoons butter in a saucepan; blend in flour. Add milk slowly and cook until thickened, stirring constantly.
Add cheese, mustard, and reserved cooking liquid. Stir until cheese melts. Add salt and pepper. Place alternating layers of green beans and sauce in a greased casserole, then top with buttered crumbs. Bake at 350° for 30 minutes.
Green bean recipe serves 4 to 6.