vichyssoise

This is good soup.

2 large leeks, while parts only sliced thinly
5 tbs butter
1 onion sliced thinly
1 lb potatoes, chopped
2 tsp lemon juice
1 tsp nutmeg
1 tsp coriander
2 bay leafs
1 egg yolk
2/3 cup heavy cream
4 cups vegetable broth

Mel the butter and add the leeks and onions about 7 minutes. Then add the potatoes, broth, nutmrg, coriander, lemon juice and bay leaves to the pan for about half an hour. After taht, remove the bay leaves and puree the soup. Meanwhile mix the yolk in with the cream and add to the soup after it has been pureed. Chill the soup and serve with chives on top and some salt/pepper.

I'd call it Vichyssoise also instead of cold potato soup.