Soupe de Poissons
Soupe de Poissons is a wonderful ingredient that only seems to be available in France, where even there, its popularity, and therefore its availability is limited to the coastal areas where it is produced. It is generally sold in jars which have a long shelf life, so snap them up where you see them.
This soup makes a fantastic base for many recipes, eg: Sous vide cod with prawns in soupe de poissons. As it often comes in 2 litre jars, it is handy that it is easily frozen in smaller amounts to use for sauces.
In the UK, the closest soup to Soupe de Poissons, is Lobster bisque.