Toss lime wedges with salt in a bowl and chill for 48 hours.
Heat oil in a frying pan and add mustard seeds until they pop.
Add garlic and ginger and stir-fry for 2 minutes.
Stir in spices and sugar until the sugar melts.
Add cured limes, juices, vinegar, and 200ml of water.
Simmer the mixture for 90 minutes until thickened and limes are soft.
Blend cooled pickle for 20 seconds and store in jars.
Mix crab coating ingredients into a thick paste.
Coat crabs in the paste and chill for at least 2 hours.
Bring crabs to room temperature before cooking.
Heat deep-frying oil to 160°C.
Fry crabs for 2 minutes until cooked and drain on kitchen paper.
Serve crabs with dollops of lime pickle.