Pierce holes through two of the "eyes" of the coconut and drain the water from it. Set the water aside. Put the whole coconut into the oven for about 8 minutes. Crack it open; the flesh should come away quite easily from the shell. Pare the brown skin from the coconut flesh with a potato peeler. Grate the coconut finely. You will need 2 1/4 cups, loosely packed, for the flan. Add the grated coconut to the reserved coconut water and boil it for about 5 minutes, stirring it constantly. Add the "condensed" milk and continue cooking for another 5 minutes. Set the mixture aside to cool. Beat the egg yolks together until they are creamy and stir them well into the coconut mixture. Beat the egg whites until they are frothy, add the salt and continue beating until they are stiff. Fold them into the mixture. Pour the mixture into the prepared mold. Cover the mold with a well-greased lid and place into a water bath. Cook the flan on the lowest shelf of the oven for about 1 1/2 hours, then test to see if it is done. When it is done, set it aside to cool. Makes 6 servings. NOTES: Of course, you can substitute1 cup of lightly thinned canned, sweetened condensed milk for the milk and sugar and substitute pre-grated but unsweetened coconut. Use milk instead of coconut water; the flavor will just not be quite as good. Do not think you have done something wrong when you see that the coconut and custard have separated. That is how it is meant to be. The caramel will nearly all have been absorbed by the spongy layer of coconut. If you are using fresh coconut there will almost certainly be some left over. It will keep perfectly well if frozen. To test to see if the flan is cooked through, insert the blade of a knife or a skewer well into the flan. The knife should come out clean. Take care not to pierce the flan at the bottom or it will spoil the appearance of the top when it is unmolded.