Cheese and Ham Soup

1 cup each onion, carrots and celery, finely chopped
1/2 cup margarine
1 cup flour
4 cups chicken broth
3 cups grated cheese
1 cup chopped ham
3/4 cup cooked potatoes
1 1/2 quarts milk
1 tsp. salt
1/2 tsp. white pepper

Sate onion carrot and celery in margarine in large saucepan. Sprinkle with lour and add chicken broth. Cook until smooth, stirring constantly. Simmer for 15 minutes. Stir in cheese. Cook for 10 minutes. Add remaining ingredients and heat.