To a mixing bowl, add cream of chicken soup, sour cream, 1/3 cup melted butter, cheese, and ham/onion if desired. Mix thoroughly.
Add in frozen hashbrowns and mix until uniform. Place mixture in desired baking dish (metal, glass, or disposable pan). There is no need to grease the pan!
If planning to make casserole at this point, to a small bowl, add one stick of melted butter and crushed cornflakes. Mix until uniform and spread on top of casserole. Heat oven to 350 degrees and bake for 45 minutes.
If freezing casserole, place one stick of butter and 2 cups crushed cornflakes in a resealable bag on top of the dish. Seal well. Freeze. When ready to bake, heat over to 350 degrees and cook for approximately 90 minutes.