Use some of the cold water to make a thin paste with the corn starch. Add the sugar, vanilla and salt to the water and boil until sugar is dissolved. Remove from heat and stir in the corn-starch mix. Return to the stove and simmer for a further 3 minutes. Remove the vanilla stick and pour mixture in a tray so that the liquid is about 3/4 inch deep. Leave to cool and cut in to 3/4 inch square cubes. Grate coconut flesh and add a pinch of salt. Roll cubes through the coconut and serve.