Vichyssoise
Perhaps the best known cold pureed soup, vichyssoise is a simple puree of potato and leeks that is traditionally enriched with cream; adding a bit of buttermilk along with the cream gives this version a pleasant tangy flavor. Here, leeks serve as both an aromatic, replacing the onion, as well as one of the base vegetables. Garlic is typically not used. The amount of stock or water called for is also reduced, since both cream and buttermilk are added. If making the soup for company, buy an extra leek to prepare the Leek Frisée (page 75) for the garnish.