Miso, also known as soybean paste, is a traditional Japanese food. It is most commonly used for making miso soup, which is served with every meal in Japan. There are different types of miso, each with a distinct and characteristic flavor. This recipe uses white miso, which has a mellow, slightly sweet flavor. Miso is available at natural food stores and Asian markets; it can also be purchased online. The shiitake mushrooms in this soup add vitamin D, an important nutrient for cancer prevention.