Bring the milk and grated chocolate to a boil in a large saucepan. Mix 1 or 2 Tablespoon. of the hot chocolate milk with the flour, and add to the soup as it boils. Stir in the sugar and remove from the stove. Add the egg yolks, stirring constantly, and return to low heat only long enough to warm the soup. Serve hot or cold in small bowls as a special dessert, with a dollop of whipped cream and a few sprinkles of chocolate or mint cordial. Serves 8