1. Put a pot of salted water on to boil.
2. Clean the crayfish tails, removing the vein.
3. Boil the crayfish tails for 6 to 7 minutes till cooked. The shell should be a deep red.
4. Remove, drain and allow to cool. In the meantime, make the salad dressing.
5. Combine together the tarragon vinegar, lemon juice, olive oil, salt and pepper.
6. Remove the crayfish flesh from the shell and cut into generous bite size pieces.
7. Fold the crayfish into the dressing, coating them well.
8. Arrange the leaves on the platter and pile the dressed crayfish on top. Serve immediately.