White miso already is packed with umami, but browning it as we do to make this soup builds even more flavor. Just a small amount of pork is enough to create a rich, porky broth; firm tofu gives the dish substance without making it heavy. Make sure to use napa cabbage, not regular green cabbage; the frilly leaves of napa are more delicate and become tender and silky after just a few minutes of simmering, but the stems will remain crisp-tender. The cabbage, tofu and scallions aren't needed until near the end of cooking, so prep these ingredients while the soup cooks. If you like, garnish with toasted sesame seeds and serve with Japanese short-grain rice.