Cook unpeeled potatoes until done. Chill. Peel and grate or slice into large bowl. Toss potatoes lightly with onion and cheese. Mix melted butter and soup together and add to potatoes. Stir in sour cream. Spread into a 1-1/4 quart casserole dish. Top with breadcrumbs. Bake at 350 degrees for one hour.
Alternative: Use hash browns instead of potatoes. Just cook hashbrowns according to package.