Vichyssoise (/ˌvɪʃiˈswɑːz/ VISH-ee-SWAHZ, French: [viʃiswaz] ⓘ) is a soup made of cooked and puréed leeks, potatoes, onions and cream.

It was invented in the first quarter of the 20th century by Louis Diat, a French-born cook working as head chef of the Ritz-Carlton Hotel in New York.

In a book published posthumously, he explained the background: I suspect that some of the fins becs [connoisseurs] who order it would be much surprised to learn of its humble origins as my mother's simple leek and potato soup.

I named my version of maman's soup after Vichy, the famous spa located not twenty miles from our Bourbonnais home, as a tribute to the fine cooking of the region.

[8] The soup was first mentioned in a French publication in 1923 in La Revue culinaire, which classified it as an item of American cuisine.

[14][15] Another important variant is the liquid in which the vegetables are simmered: rather than Diat's light cream and milk, chicken stock is specified in recipes by Simone Beck, Louisette Bertholle and Julia Child, in their Mastering the Art of French Cooking (1961),[16] Craig Claiborne (1969),[14] and Anne Willan (1994).