Creamy Potato Soup

3/4 cup butter 5 cups potatoes, cooked and cubed
3/4 cup flour 1 cup celery
1 tsp salt, pepper to taste 1/2 cup onion
3 cups milk 2 cups grated cheese
3 cups chicken broth

Heat butter on medium heat until melted. Add flour, salt and pepper and whisk until smooth and bubbly. Remove from heat. Gradually whisk in milk, then broth. Add potatoes, celery, onions and cheese. Cook until creamy and cheese is melted.