6 sweet potatoes, peeled and cubed
2 leeks, chopped
2 onions, chopped
4 stalks celery, chopped
2 cups low-sodium chicken broth
1 Tbsp parsley flakes
1 tsp tarragon
5 cups water
1 tsp black pepper
1 13 oz can fat-free evaporated milk
2 Tbsp chopped chives