Cook noodles as directed on package; drain.
While noodles are cooking, combine in a small saucepan the soup and milk, stirring over low heat until smooth. Add onion, mustard, and sour cream. In a greased 1 1/2 quart casserole, layer half of the noodles, half of the ham and sauce. Repeat layers. Toss bread crumbs with the 1 tablespoon melted butter and sprinkle over the casserole. Top with grated cheese.
Bake, uncovered, at 325° for 25 minutes, or until golden brown and bubbly.
Calories per serving: 414
Fat per serving: 27.3g