Put the crab on its back on the chopping board, so that the claws and softer body section face upwards, then simply twist off the main claws, leaving the legs attached to the body. Now put your thumbs against the hard shell, close to the crab’s tail, and push and prise the body section out and away from the shell. The legs should still be attached to the body. Remove the small stomach sac situated just behind the crab’s mouth and pull away the feather-like gills (‘dead man’s fingers’) which are attached along the edges of the centre part; discard these.
Using a teaspoon, scoop out the brown meat from inside the shell; reserve.
Chop the body into quarters and then cut the main claws in half at the joint. Crack the shells of each piece with a hammer or the blunt edge of a large knife.
Heat the oil, garlic, ginger and chilli in a wok for one minute to release their aromas.
Next, turn up the heat and fry off the brown crab meat, then add the ketchup, soy sauce, Marmite and 150ml of water. These all add savoury and sweet notes to the finished dish. Now add the remaining crab in its shell and stir-fry the crab for two minutes. Remove from the heat and finish with spring onions and chopped coriander.
Serve immediately – with lots of finger bowls and napkins, as this is a messy dish.