Soak the fish in an earthenware or porcelain dish for 36 hours, changing the water frequently. Drain it and pat it dry with kitchen paper. Skin and fillet the fish and slice it very thinly.
Heat the walnut oil in a frying pan and when it starts to smoke, tip in the fish. Reduce the heat slightly and stir briskly, turning the fish over and over. It will break up and soften and as you con