This traditional chinese sweet soup recipe is made with black sesame seeds and is rumored to help prevent gray hair. It is eaten warm after meals as a dessert or as a mid-afternoon snack and, of course, at dim sum. It's especially popular in hong kong and southern china. Feel free to use chinese rock sugar (available at asian markets) instead of granulated sugar if desired. While the soup is delicious on its own, for an added touch, it can be garnished with crushed nuts, shredded coconut, or softened chopped chinese dates.