Although we generally think of them as a favorite Japanese food, adzuki beans are believed to have been domesticated in the Himalayas several thousand years ago. By 1,000 B.C. they appeared in China, then later in Japan, where today they are second only to soybeans.
They are small and cook quickly, and the tannins in their skins give the soup added color and flavor. This light miso soup is perfect for those occasions when you want to take the edge off your appetite without stuffing yourself to the gills, or when you want a lot of broth with just a little bit of substance to it.
You could also add some small cubes of tofu for extra protein.
Rinse the adzuki beans thoroughly, then place them in a 7-quart slow cooker along with the water and miso. Stir.
Cover and cook on low for about 4 hours or until the beans are tender. Add the tofu (if using) and continue cooking for 15 more minutes or until the tofu is hot.
Ladle the soup into bowls. Top each bowl with the sliced scallions and serve.