An elegant French soup made with mussels, onions, wine, cream and seasonings. The mussels are strained out of a classic billy bi, leaving a smooth and silky soup. However, today it is often served with the mussels. Though there are several stories of the soup's origin, the most popular is that Maxim's chef Louis Barthe named it after a regular patron who particularly loved the soup, American tin tycoon William B. (Billy B. ) Leeds.