Wash and clean the crabs if required and add the Turmeric and rub this all over the crab
Lightly toast the dried chillies, cumin & coriander seeds and peppercorns, cool and then grind to a powder
In a food processor add the garlic, onions and coconut
Add the turmeric and the tamarind and start with 1/2 cup of water and process
Strain this separating the liquid from the solids
Process the solids adding more water 2 - 3 times till you get a nice bowl of silky gravy
In a large pot, melt the coconut oil and saute the diced onion and slit green chillies
Add the crab and allow it to roast for a minute and then pour the silken gravy over and allow the crabs to cook for 15 - 20 mins
Add salt to taste