Heat the ghee in a saucepan, add the shallots and fry 5 minutes. Sprinkle over the flour and reduce heat to low.
Slowly add 2 cups water, mixing to avoid lumps. Stir in tomato paste, chilli powder, coriander, turmeric and salt. Bring to a simmer then add the fish. Simmer, covered, 20 minutes, stirring occasionally.
Remove from the heat. Pour in the coconut milk and stir well. Add vinegar and black pepper and serve.