1pound sweet potatoes, peeled and cut into 2-inch chunks
1/2 teaspoon salt, plus more to taste
3cups cooked or canned white or black soybeans
2pounds napa or savoy cabbage
2/3cup any miso paste, plus more to taste
1/4cup chopped scallions
1 tablespoon sesame oil
Instructions
Put 8 cups water in a large pot and bring to a boil over medium-high heat. Add the sweet potatoes and salt and cook, stirring once or twice, until they’re tender on the outside but still firm at the center, 10 to 15 minutes. If you’re using canned beans, rinse and drain them; if homemade beans, just drain them.
Add the cabbage and cook, stirring occasionally, until just barely tender, 2 or 3 minutes. Turn off the heat.
Put about 1 cup of the cooking liquid in a small bowl and add the miso; whisk until smooth. Stir the miso mixture into the liquid in the pot and turn the heat to medium.
Add the beans; stir once or twice and let sit for a minute, still over medium heat, just long enough to heat everything through without letting the soup come to a boil. Taste and adjust the seasoning, adding more miso (whisked with some of the soup) and salt if necessary. Add the scallions, drizzle with the oil, and serve.