Melt the chocolate, together with the cup of water, in a saucepan over a low heat, taking care it doesn’t burn. Keep stirring all the while, or else your hot chocolate will develop an unpleasant overcooked taste. Add the salt and almost all the walnut drink (save some for later).
Dissolve the cornflour in the walnut drink you saved earlier and add to the mixture. Stir well to prevent any lumps forming. Keeping stirring for a couple of minutes more until it starts to thicken.
Take off the heat and add sugar to taste, bearing in mind that the walnut drink already adds some sweetness itself.