Trio of orange vegetables soup

This soup that i threw together last night turned out so good I want to jot down the recipe before I forget it.

2 T. olive oil
1 large onion, roughly chopped
2 large leeks, cleaned and roughly chopped
4 large carrots, peeled and roughly chopped
4 stalks celery, roughly chopped
1 large sweet potato, peeled and chopped into large pieces
1.5 cups pumpkin puree (1 small can)
2 sticks fresh rosemary, leaves stripped and chopped
salt and pepper to taste
6 cups water (or vegetable broth)
2 T. white balsamic vinegar
1/4 c. heavy cream, optional (or coconut milk, or 2 T. butter)

Heat olive oil in large soup pot over medium to medium high heat. Saute onion with a sprinkling of salt for a few minutes, then add leeks. Stir frequently until slightly softened and browned. Add carrots, rosemary, and celery and saute a few minutes more. Add sweet potato, 6 c. water, and pumpkin (or more water, if this doesn't seem like enough). Bring to boil, and simmer until vegetables are soft, about half an hour. Turn off heat and puree with an immersion blender until smooth, but not too smooth. There should be some texture and small pieces of vegetables in the soup. If too thick, add a bit more water. Add salt, pepper, and vinegar to taste. Stir in cream, coconut milk, or butter if desired.

I added the heavy cream as an experiment, since i have some left over from thanksgiving. Even a small amount of cream adds a lot of rich flavor. But the soup is very good without also. A little butter or coconut milk would have the same effect. A topping of sour cream or plain yogurt would be nice as well.