Cucumber Vichyssoise with Crayfish Cream

The word vichyssoise is used loosely here to mean a chilled cream vegetable soup that is thickened with potatoes and enriched with cream, along the lines of the original one of Louis Diat. The cucumber provides a nice change from leeks, and you could use summer squashes as well, or even eggplant. If you do not want a shellfish cream, use the tomato cream.