In a large heavy pot, combine all the ingredients above the line. Bring to a boil, then cover, lower the heat to medium-low, and simmer for 30 minutes. Remove the mushrooms and slice thinly, discarding the tough portions. Strain the broth and return it to the pan. Add the tofu and mushrooms and simmer for 5 minutes. Dissolve the miso in a small amount of the broth, stir it into the soup, then immediately remove the pot from the heat. Garnish with minced garlic chive leaves and serve at once.
Substitution for the Chinese garlic chives: 1 clove garlic and twice as much volume of fresh chives.