Bring a pan of water, large enough to hold the 4 crabs with plenty of room, to the boil. Season the water with the salt, peppercorns, bay leaves and lemon. Add the crabs upside down–so the claws will not break off–and bring the water back to the boil. Boil for 5 minutes, turn off the heat and leave the crabs in the water for 15 minutes, then plunge them into cold water, drain and leave to get cold.
Remove all the white meat from the body. Leave the brown meat inside the shell and be careful to discard the possibly poisonous dead men’s fingers. These are gills which filter water, the purity of which cannot be guaranteed. Return the white meat to the body shell, crack the claw shells to expose the meat.
Make the dressing with the lemon juice, extra-virgin olive oil, chopped parsley, garlic and salt and freshly ground black pepper to taste. Mix ingredients with a fork to amalgamate well. Spoon the sauce over the crab body and claws.