Oven preheat 400 degrees
Bring 4 quarts water and ham to a boil in large pot. Once water boils remove ham to plate. Return water to boil and add onion and macaroni cooking for 8 minutes, drain and return to pot.
In same pot add ham, cheese, sour cream and soup.
Scrape into 13x9 casserole dish. pour melted butter on top and add bread crumbs.
bake for 30 minutes until heated through, uncovered.