Cut the fish into smaller pieces, however you want, and sprinkle lightly with salt. Put the sultanas in a bowl, strew with the saffron, warm up the sherry and pour it over. Put a thick-bottomed frying pan on the heat and toss the pine nuts in it until they take on a deep gold color and give off their waxy aromatic scent. Pour onto a plate and put on one side. Pour the sultanas in their saffroned sherry into the emptied-out pan and add the water, then put it back on the heat and let it come to a simmer, then add the fish fillets, or as many as will fit in one layer; add more water if they are not more or less submerged. After about a minute’s simmering, turn them over with a couple of spatulas. They cook very quickly and if you leave it too long, they’ll flake as you turn them. Give them another minute or so on the second side and remove to a waiting plate. Continue till you’ve used up all the fish, adding more water as necessary. When you’ve finished, use the spatula to remove as many sultanas as you can to the cooked fish on the plate, then turn the heat under the frying pan to high and let the sherry-saffron juices reduce till you have a just-liquid yellow syrup. Pour this over the fish, then scatter over the toasted pine nuts. And that’s all there is to it.