Once the crabs are cleaned and cut into pieces, marinate with salt and turmeric powder, set aside for about 20-30 minutes.

In a mixer grinder add the whole chillies, garlic, ginger, coriander, cumin and mustard seeds. Blend into a coarse paste with some water (just enough to mix). Once blended, add in the coconut and the tamarind paste but only blitz for about 5 seconds so that the coconut is still rough.

Heat the oil in a pan. Add the finely sliced onions and fry until softened. Add the prepared ground spices and cook for a couple of minutes on a medium to low heat, stirring regularly. Add the curry leaves and cook out for a couple of minutes.   

Add the crabs along with warm water and cover to cook. This should take about 10-15 minutes. Season to taste.

5. To serve, garnish with chopped coriander leaves and sliced chilli. Serve immediately.