I'm a week late! Ack!
I've never had vichyssoise before but I guess this soup would be similar, as they're both pureed potato and leek soups, however this soup is served hot and is probably not as thick as vichyssoise, and obviously vichyssoise does not have cilantro in it.
It's delicious and easy to make, although sometimes it can be a pain to have to puree a large amount of something.
This recipe is from 101 Meatless Family Dishes by John Ettinger, published in 1995.
3 tbsp butter
4 cups (about 1 pound) leeks, trimmed, cleaned, and chopped*
2 stalks celery, sliced**
3 cups water
2 potatoes, peeled and diced
3 cups milk
1/8 tsp salt
1/4 tsp pepper
1/2 cup chopped cilantro (optional, or you may use parsley or watercress instead)
*One leek will yield 1 to 1 1/2 cups chopped (white part only).
**I chose to omit the celery as I don't like the taste of cooked celery all that much.
Melt butter in a large pot, add the leeks and celery, and cook over low heat 15 minutes, stirring frequently.
Add water, potatoes, milk, salt, and pepper. Cover and cook on medium-low heat for 20 minutes, stirring frequently, or until potatoes are tender.
Remove to a blender or food processor and puree. Stir in cilantro, or sprinkle on top and serve.