Potato-Cheese Soup

6 medium potatoes, peeled and sliced
4 tablespoons flour
1 teaspoon parsley
1 teaspoon salt
2 cups Swiss cheese, shredded
1 small onion, chopped
2 cups milk
6 tablespoons butter

Add potatoes and onion to 2 cups salted boiling water. Cook about 20 minutes, mash potatoes slightly (don't drain). Add enough milk to make 5 cups. Add other ingredients, except cheese. Stir until thickened. Add cheese and stir until melted. Thin with more milk as needed.