When you have squeezed out every drop of liquid from the ground coconut mixture, add another half cup of warm water to the coconut mixture and put it into the blender or mixer once more, then through the sieve, so that all the milk has been extracted. Now put the coconut extract into a deep pan on a medium heat and stir cook for 30 minutes, till the sauce becomes thick. Add the marinated prawns or fish and the tamarind pulp to the boiling sauce. Stir cook, adding more salt if necessary. When the fish curry is reduced to half its quantity, remove the curry and put it into a serving dish.