Potage Billy By (Cream of Mussel Soup)

According to the 1962 cookbook Chez Maxim’s: Secrets and Recipes from the World’s Most Famous Restaurant, presented by the Countess of Toulouse-Lautrec, the variously spelled soup Billy By originated at the restaurant Ciro’s in Deauville in 1925. William Brand (Billy B.) wanted to spare his well-off American friends from having to eat mussels from the s…