If you're cooking a live crab, first bring a large pot of well-salted water to the boil. (If using a ready-cooked fresh crab, proceed to the next step.) Add the crab to the pan and boil for 20-30 minutes. Remove from the water and stand on its nose to allow the water to drain away as the crab cools.
To prepare the cooked, cooled crab, first remove the legs by twisting them off where they meet the body.
Remove the claws by pulling them off from the body.
Separate the crab body from the central part of the crab by placing the crab on its back (hard shell-side down). Put your hands under the edge of the crab and push upwards until you hear it break. You may need to use a heavy knife to help you lever the crab apart.
Remove all ten of the spongy 'dead men's fingers' and discard.
Drain any excess water from the shell of the crab and remove the stomach sac and hard membranes inside the shell.
Use a spoon to remove the brown meat from the shell and any soft shell that has formed. Place it into a clean bowl and mash with a fork.
Press down on the edges of the crab shell, breaking away the outer edges to form a 'dish' for serving.
Break each claw in half. Use the handle of a teaspoon to scrape the white meat out of the thick end of the claw. Place into a separate clean bowl.
Use the back of a heavy-bladed knife to crack open the remaining piece of claw and the pincers. Remove all the white meat and flake into the bowl. Remove the piece of cartilage inside each of the claws, pick off the meat and discard the cartilage.
To remove the meat from the body of the crab, take a sharp knife and cut the crab body in half then in half again. Pick out the meat using your fingers.
If the legs are large enough, it's worth picking the meat out of them. Snap them in half and discard the thin end of the leg. Using the back of a heavy-bladed knife, smash the shell on the thicker part of the leg. Pull the meat out and add to your bowl.
Run your fingers through the white meat in the bowl to break up the meat and to pick out any remaining bits of shell.
Return the prepared white and brown meat to separate halves of the prepared crab shell.
Serve on a plate with some good-quality mayonnaise, some brown bread and a wedge of lemon. Garnish with fresh parsley, if you like.