Bring a suitable pan of salted water to the boil. Add 5 of the langoustines and cook for 5 seconds. This is done in small batches so the water doesn’t cool down too much. Take out the langoustines and plunge into a bowl of ice water. Repeat this process 3 more times.
When cool, remove the shells so you are left with the tail meat. The shells, along with the heads and claws, can be used