1. In a large bowl combine turkey, ham and cheese; set aside.
2. In a saucepan, saute onion in butter until tender.
3. Add flour; stir to form a paste.
4. Gradually add cream and stir constantly.
5. Bring to a boil; boil 1 minute more until thick.
6. Add dill, mustard, and nutmeg; mix well.
7. Remove from heat and pour over meat mixture.
8. Spoon into a greased 13inch x 9inch x 2inch baking dish.
9. Toss breadcrumbs, butter, and dill; stir in cheese.
10. Sprinkle over the casserole.
11. Bake uncovered at 350* for 30 minutes or until heated through.