To make dashi, add water, kombu and dried shiitake mushrooms to a large stock pot. Heat to a gentle simmer, then remove from heat, cover and let sit for 30 minutes. After 30 minutes, remove the kombu and dried mushrooms with a slotted spoon (or strain the broth through a fine mesh sieve).
Bring the dashi to a gentle simmer. In a small bowl, whisk together miso paste and ½ cup of warmed dashi and set aside.
Add the miso/broth mixture, soy sauce, green onion, mushrooms and bok choy to dashi and let cook over low (don't boil) for 5-10 minutes, until the vegetables soften.
Add tofu and serve, or add tofu to each individual bowl and serve with the miso soup.
