Cut the tofu: Gently slice tofu into bite-sized cubes. If using silken tofu, handle carefully so it doesn’t break up. Cut green onions as well, set aside.
Prepare the broth: Add water and dashi powder to a medium pot. Warm over medium heat until the dashi is dissolved. Let it simmer lightly for a few minutes to develop flavor, then reduce heat to low.
Add dried seaweed/wakame: Measure and add dried seaweed directly into the pot. Be precise when measuring as it expands significantly in volume once rehydrated.
Warm the tofu in the broth: Add the tofu cubes and warm them through. Keep the heat gentle — just warming, not boiling. Add green onions.
Turn off the heat and dissolve the miso: Turn off the heat completely. Put miso in a ladle, add a little hot broth, and whisk until smooth. Stir the miso slurry back into the pot.
Serve immediately: Ladle the soup into bowls and enjoy warm. Miso soup is best fresh — the texture and brightness are at their peak right after making it.