In ancient China, the soybean was considered to be one of five sacred grains, along with barley, millet, rice, and wheat. Here, in the form of tofu, the soybean shines with a little help from miso, spinach, carrots, and scallions.
Be sure to purchase firm or extra-firm tofu for this soup, as it will hold up better in hot liquid than softer varieties. Because the flavor and healthful qualities of miso are affected when boiled or with prolonged exposure to high temperatures, it should only be added at the end of cooking. Whisk it with a bit of liquid first so that it is quickly and evenly distributed. We used white miso in this soup, as it is lower in sodium, but you can use darker types for a stronger, more pronounced flavor.