Goan fish curry

Method

1. Roughly grind the dried spices together in a mortar and pestle, then place in a large bowl and add the coconut and garlic. Mix well, then add enough water to make a loose paste. Working in batches, put the paste in a blender or the bowl of a food processor and process for 3–4 minutes.
2. Transfer the coconut spice paste back to its original bowl. Using your hands, squeeze out all the liquid into the bowl. Discard the squeezed out coconut and spices, but keep the liquid. Strain the liquid through a sieve into a large saucepan with a lid to get rid of any remaining flakes of coconut. Add the grated onion to the pan and place over a high heat. Bring to the boil, reduce the heat to low and simmer briskly for 15 minutes. (At this point, you could cool and store in the fridge or freezer until ready to cook.)
3. Just before cooking the fish, heat the oil in a pan over a medium heat. Add the mustard seeds and when they begin to pop add the curry leaves and let them sizzle for a minute or so. Remove from the heat but keep warm.
4. Add a couple of pinches of salt and 1 tablespoon of the white wine vinegar to the coconut sauce, and taste. Add more of both, if necessary – the curry should be spicy, full of flavour and gently tangy. When ready to serve, bring back to a simmer and add the prawns and white fish. Cook for 3–4 minutes, spooning the sauce over the fish, until the prawns are pink and the fish is cooked through.
5. Serve the curry sprinkled with coriander leaves, alongside steamed rice drizzled with the tempered seeds and curry leaves.