Not that I order vichyssoise in restaurants any more--I've never had a proper vichyssoise in a restaurant. Which baffles me, it's about the easiest soup there is to make. The problem is, I'm not good at planning ahead unless I'm cooking for guests, and this is a soup that has to be chilled after cooking--so it's been a long time since I've made it.
3 cups sliced leeks, thoroughly cleaned (or a mix of leek and onion)
4 cups red potatoes, peeled and diced
8 cups water (some of this could be chicken stock, but even if I ate chicken I'd use water)
1 Tbs salt
3/4 - 1 c heavy cream
Put the first 4 ingredients in a pot, bring to a boil, and simmer, partially covered, 50 minutes. Remove from heat and let cool. Purée--a fine food mill is best for this, a blender or stick blender is next; don't use a food processor, it'll turn glue-y. Taste for salt--because it's chilled it needs to be a little saltier than you'd think. Chill. Check the texture, you may want to add more cold water. Add the cream before serving and garnish with snipped chives. Glorious.