Put cubed potatoes in large pot and cover with water (to where they're just barely covered -- don't put in extra). Add onion, celery, salt, pepper, bullion and parsley. Boil until potatoes are just tender. Whisk flour into cold milk -- once well blended, add mixture to pot (on medium heat). Stir frequently until soup thickens a little. Once it's as thick as you like, add the cheese and ham. Stir well and simmer for a couple of minutes and serve!