I like adding tilapia filets to this soup because they lend a subtle sweetness and extra 'umami' to the dish. And, since tilapia is so mild, you won't get any of that 'fishy,' oily taste, which some people might find overpowering or unappetizing. But, if you don't like fish, by all means leave it out. Traditionally, you would strain the soup to get a clear broth, but I like leaving the bonito shavings in because I like their texture and taste. IMHO, miso soup tastes even better the next day because the tofu will have had more time to absorb the flavors of the broth.
For the DASHI:
30 cups water
2 oz. dried kelp (Kombu)
6 packets (2 cups) of shaved dried bonito (Katsuobushi)
1/2 cup Mizkan Seasoning Sauce (Umami Dashi Tsuyu), or 2 tbsp. soy sauce (optional)
3 14-oz. boxes of soft or silken tofu, cut into 1" cubes
8 scallions, thinly sliced
2 lbs. tilapia fillets, edges and bloodlines along the middle trimmed; cut into 1" pieces (optional)
1 cup white miso paste (shiromiso)
1/4 cup dried Wakame seaweed
1. Combine the water and kombu in a stock pot and bring to just a boil over medium low heat (15-20 minutes). Remove the kombu from the stock. Do not cook the kelp too long or the soup may end up being a bit slimy.
2. Add the shaved bonito and Mizkan Seasoning sauce or soy sauce to the kombu stock. Reduce heat and simmer for 10 minutes.
3. Add the tofu cubes to the broth and half of the sliced scallions and simmer for 20 minutes.
4. In the meantime, add 1/4 cup of the hot broth to the miso paste and stir well.
5. Add the Wakame to the soup and cook 4-5 minutes the Wakame has rehydrated.
6. Stir in the miso paste and fish. Heat the soup until it just hot, but not boiling. Do not boil, or else the miso will become granular/gritty. Once the fish is cooked through, add the rest of the scallions, and ladle into individual serving bowls.
As I mentioned before, this soup tastes even better the next day. Just remember not to boil the soup when reheating so that the miso doesn't precipitate.
Add the wakame to the soup and cook about 5 minutes or until the seaweed is rehydrated.