Bring the dashi to a slow boil over medium heat. Once boiling, turn off the heat.
4 cups Dashi
Add the miso, 1 tablespoon at a time, ensuring the miso is completely dissolved before adding more. You may see some koji floating in your broth after dissolving the miso. That is completely normal but you can remove it with a fine mesh sieve if you prefer.
4 tablespoons miso
Gently add the tofu to the soup. Be careful not to stir too aggressively at this point or you will break the tofu.
7 ounces soft/silken tofu
Add the wakame seaweed and sliced green onion, stir to combine, and serve immediately. If you have leftovers, when reheating, don't bring the soup to a boil or you will lose a lot of flavor and aroma.
1 tablespoon dried wakame seaweed, 1 scallion/green onion sliced thin