Despite its French name, this cold soup was invented in New York City to commemorate the opening of the roof garden at the old Ritz Carlton hotel in 1910. It is a wonderful soup and excellent hot as well as cold.
Wash and drain the leeks. (Save the green parts for another dish.) Place the leeks, potatoes and onion in a saucepan. Add the stock and simmer, covered, for 35 minutes or until the vegetables are very soft. Sieve or purée in a liquidiser or processor. Stir in the cream and season well with salt and pepper. If you are serving the soup cold, chill and serve in chilled bowls, garnished with lots o