Ham and Potato soup

3 1/2 cups peeled and diced potatoes
1/3 cup diced celery
1/3 cup finely chopped onion
1 cup diced cooked ham
3 1/4 cups water
2 tbsp chicken bouillon granules
1/2 tspn salt
1/2 tspn pepper
5 tbsp butter
5 tbsp flour
2 cups milk

combine the potatoes, celery, onion, ham and water in a pot.  Bring to a boil, then cook over medium heat until potatoes are tender.  Stir in chicken bouillon, salt and pepper.  In a separate saucepan melt butter and whisk in flour with a fork, stirring constantly until thick, about one minute.  slowly stir in milk so lumps don't form. continue stirring over medium-low heat 4-5 minutes. stir the milk mixture into the pot with potatoes until heated through.  serve immediately.