This soup is traditionally made with chicken stock, but here I used miso (fermented soybean paste) to give an intense flavor. Miso is like a vegetarian bouillon. Different types of miso range in strength and color
Light ones are young and mild, while darker misos, which have been aged longer, are saltier, richer, and more intense. In this recipe I call for a mellow white miso, which has only been aged for about four months. You can substitute a red miso (aged for six to eight months) to bring it up a notch. Anything darker would overpower the soup.