To read more about miso, see here. There are many kinds available, especially in Japanese groceries. We often use a combination of red and white miso for this soup.
If desired, soak in cold water for 10 minutes:
Meanwhile, heat in a medium saucepan over medium heat:
Once at a low simmer, add:
(Save the stems for stock or another use.) Cook over medium-low heat for a few minutes to cook the mushrooms. While they simmer, place in a small bowl:
Add about ¼ cup of the warm dashi and whisk to dissolve the miso. When the mushrooms are cooked, whisk this mixture back into the soup. If using the wakame, drain it and divide among 3 soup bowls, along with:
Ladle the broth and mushrooms into the bowls.