Potato soup even my toddler likes!

Caution: this is not necessarily a toddler-friendly recipe! My girl isn't a very picky eater. But we all think this soup is yummy. And it's filling!

Saute in a heavy pot:
1 medium onion
3 stalks celery, finely chopped (include leaves)

Add and cook until tender:
3 medium potatoes (or 2 large), peeled and diced
3-4 cups water or stock
salt and pepper to taste
1 small bay leaf

Let cool briefly. While stirring with a wire whisk, add:
1 cup instant dry milk
1-2 tablespoons butter

Reheat but do not boil. Add salt and pepper to taste and garnish with parsley or green onions.