Vichyssoise is a chilled leek and potato soup that was first introduced to Americans in the summer of 1917 by a French Chef at the Ritz Carlton in New York City as a way to help cool the patrons. It is best to serve the soup slightly chilled, but not cold, as the intensity of the flavor lessens as it gets colder. In the cooler months the same soup can be served hot and is very satisfying on a cold winter night.