Place the tamarind slices in about 150ml hot water and soak for 30 minutes, drain and reserve the liquid.
Place the garlic and ginger in a food processor and blend until a smooth paste forms. Set aside for later.
Remove all of the meat from the crab. You can pull the crab apart into segments to make this easier: begin by pulling off the front claws and legs and using a crab pick and shell cracker to get the meat out. Pull the body apart, remove and discard the gills and internal organs, then pick out the white meat.
Warm the oil in a large deep saucepan or wok over a medium-low heat. Add the curry leaves cumin, tomato, onion, crab, turmeric, ginger and garlic paste and mix well.
Add the chilli powder and half of the remaining water, followed by the mutton masala, fish powder, kurma powder, garam masala and reserved tamarind water. Add salt to taste and the remaining water. Give a good stir then cover and allow to cook until the sauce reduces and thickens, about 20 to 30 minutes
Once thickened, add coconut milk, coriander leaves and sugar. Bring to the boil then remove from the heat and serve.
Please be sure to get the curry consistency right for bread and rice. Before adding on to coconut milk the curry should be half thick. Taste for Salt. I'm using Baba Brand Spice powder. Enjoy!!