Originally found off the coast of Norway (which is how they acquired their other name, Norway lobster) langoustine are a member of the lobster family and are closely related to Dublin Bay prawns and scampi, for which they are often mistaken. These days they are caught along the Atlantic coast, including Scotland, as well as the western Mediterranean and the Adriatic, though overfishing has meant that they are extremely rare, and even more of a delicacy than they were previously.
Unlike other crustaceans, langoustine don't change colour when they are cooked. They have pink, narrow smooth-shelled bodies, with long knobbled claws, and tend not to carry much meat. The shell, head and thorax (the upper torso) can't be eaten, but the tail and the meat in the claws can. As they go off very quickly, most langoustine are cooked and frozen at sea, which means it's quite hard to find live ones.
All year round.
Choose the best
If buying live langoustine, make sure they are still moving. Larger langoustine are better value, as they'll have more meat on them. Avoid those whose tails have started to turn black - they're dead. As a rule of thumb, the colder the waters in which the langoustine were fished, the better their flavour, which is why Scottish langoustine are particularly prized.
Pre-cooked langoustine should be thawed (if frozen) - then they are ready to eat. Live langoustine should be cooked as soon as possible after buying them. If you are squeamish about cooking them live from raw, the most humane method is to rinse them, then put them in the freezer or in a dish and cover with crushed ice for 1-2 hours. This renders them unconscious. They should be cooked whole.
Either grill (1 minute on the first side, then 30 seconds on the other) or boil (immerse live in boiling water and boil rapidly for 2 minutes. Then, to stop the cooking process, plunge into cold water and leave for 3-4 minutes. Then break off the head and thorax (they should be discarded). To eat the tail, peel off the shell. To eat the meat in the claws, crack them open - long metal lobster picks are useful for picking out all the meat inside.
Until you are ready to cook your langoustine, keep them in a box in the fridge covered with damp newspaper. Use live langoustine as soon as possible after buying them - preferably the same day. Cooked langoustine can be kept in the fridge for up to two days.
Boil or grill and serve with mayonnaise and lemon juice.