
Make the fermented soybean paste: Soak the soybeans in plenty of water for 12 hours. Drain, transfer to a large pot, cover with fresh water, and simmer for about 6 hours, or until very soft. Drain well, then mash the beans while still warm. Dissolve the mature miso paste in the warm water, mix it into the mashed soybeans, and spread the mixture about 2 inches thick in a clean pan. Cover tightly and keep in a warm place at 104°F (40°C) for 24 hours to ferment. Transfer to clean containers and refrigerate until ready to use.


Make the soup: Bring 4 cups water and the shrimp shells, heads, and tails to a boil. Skim off any foam, then reduce the heat and simmer for 45 minutes. Strain the broth into a clean saucepan. If using dashi powder instead, dissolve it in 4 cups boiling water. Whisk in 1 tbsp of the fermented soybean paste, then add the seaweed, tofu, bok choy, and garlic chives or green onion. Simmer gently for 2 to 3 minutes, then season to taste with a few drops of fish sauce and soy sauce. Serve hot with pickled ginger on the side.






