Soak the seaweed in a bowl of water. Let it sit and set aside until the end.
In the meantime, cut the carrot and spring onion into small pieces.
In a saucepan, heat up 1 cup of water. Add the carrot and onions and let it boil for 7 to 10 minutes until the vegetables are al dente.
Add 5 more cups of water to the saucepan and bring it to a boil one more time, then reduce the heat, and let the broth simmer. In the meantime, take out 1-2 cups of this broth and pour it into a small bowl. Let it cool down for 3-5 minutes. Then stir in the miso paste and whisk it until the miso is completely dissolved.
Finally, turn off the heat, and add the dissolved miso to the main broth in the saucepan. Add tofu. Rinse the seaweed and add it too.
Divide the soup into individual bowls and serve it hot.