Heat the water in a saucepan and cook the garlic, ginger, sugar, soy sauce and thai fish sauce over high heat for 5 minutes. Add the lime juice, the chilli. To thicken the sauce, mix a spoonful of the indian corn flour and water together to form a thin paste and add slowly to the sauce until it thickens. To add colour and flavour to the sauce, add the spring onions and coriander at the last minute.
Take the white meat out of the crab’s claws and mix with the rest of the soft meat. Once the crab has been dressed, pour the sauce over the meat and bake in a hot oven for 10 minutes until golden.