Grind Cummin, pepper, turmeric and coriander first, then crush the coconut on the grinding stone. Take them out, pour 1/2 cup of water first and 1 cup of water 2nd time and draw the milk.
Fry half the onion in oil till brown and then add the other half, garlic, slit green chillies and tomato. Stir well and add fish and salt. Carefully stir for sometime. Pour the 2nd milk, put the lid on and slowly cook till the gravy is reduced. Add the first milk and the vinegar and allow it to simmer without the lid. Before removing sprinkle some minced coriander leaves.