Ham and Potato Soup

3 1/2 cups peeled and diced potatoes (1 3/4 pounds)
1/3 cup diced celery
1/3 cup finely chopped onion
3/4 cup diced cooked ham
3 1/4 cups water
3 chicken bouillon cubes
1/2 tsp salt
1 tsp freshly ground black pepper
5 Tbsp butter
5 Tbsp flour
2 cups milk

Combine potatoes, celery, onion, ham and water in a stockpot.  Bring to a boil, then cook over medium heat until potatoes are tender, about 10-15 minutes.  Stir in the chicken bouillon cubes, salt, and pepper.  In a separate saucepan, melt butter.  Whisk in flour with a fork and cook, stirring constantly, until thick, about 1 minute.  Stir in milk slowly, so as not to allow lumps to form, until all the milk has been added.  Continue stirring over medium low heat until thick, about 4-5 minutes.  Stir milk mixture into stockpot and cook soup until heated through.  Serve immediately. 

Makes 8 cups