If, over the summer, you are anywhere near Newlyn fish market, make a detour to H.Harvey & Sons shellfish shop (www.crabmeat.co.uk). Here, freshly boiled crabs are lined up under chipped ice. Near by, just past the harbour full of fishing boats, is where you buy live crabs from huge concrete tanks. It's a staggering sight; hundreds of different-sized crabs doing their sideways crawl, as well as crayfish, lobsters and long-legged spider crabs.

When buying live or boiled crab choose one that feels proportionally heavy for its size with a dark, hard shell, that shows it hasn't cast it shell recently. Chose a feisty, lively crab waving its antennae and looking around for a fight rather than a docile one that seems resigned to its fate.

On average the yield of meat from a crab will be one third of its weight and about two thirds will be brown meat. Male crabs have larger claws than the female and, as it's the claws and legs that contain most of the white meat, males are generally thought to be the best buy, though the meat from females is sweeter. The sex of a crab is determined by its tail, which is curled up under the body. The female is broad and round while the male is narrow and pointed.

It is always best to buy live. Live crabs should be cooked as soon as possible but can be kept, covered with a damp tea towel, in the bottom of the fridge for a couple of days if they were lively when you bought them. Keep an eye on them though and if they die, cook them immediately because crabmeat deteriorates extremely fast once the crustacean is dead.

There is much debate about the most humane way of killing. At Harvey's they suggest quickly stabbing the crab under the flap below its eyes. Wait ten minutes and then cook it in a very big pan of vigorously boiling, generously salted water. A good-sized crab weighs an average 1kg to 1.5kg and takes 20 minutes to boil in approximately 5 litres of water with 1tablespoon of salt. For smaller crabs, up to 900g, allow 15 minutes. The cooking time starts when the water returns to the boil.

Once boiled, leave to drain and cool in the sink and then transfer to several sheets of newspaper to be dealt with. Place the crab on its back and, using your fingers, twist the claws from the body. Twist off the bony tail flap and discard. Pry the body from the shell by pressing hard with the full weight of your thumb opposite the eyes where the carcass obviously dovetails into the shell. Remove the stomach bag and grey, crepey “dead man's fingers”. Remove the legs and cut the body in two. Cut each half in two again, cutting across to expose the meat in the leg chambers. Scrape the firm, creamy meat round the edge of the shell and then the brown meat and slush in the middle into a small bowl. This is extremely rich and tasty.

Season with salt, pepper and a little vinegar or lemon juice. Crack the claws and legs slightly - we use a small wooden mallet but special claw crackers are available from any cook shop - taking care not to crush the meat inside.

This is a hands-on greed-fest. All the preparation can be done in advance; the cooking is fast and furious. Crab is very rich so serve with boiled basmati rice and simply cooked green beans.

Crab with ginger and spring onion

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