Place the kombu and water in a pot over medium heat. Just before it comes up to a boil add the bonito flakes and turn off the heat.

Let the kombu and bonito sit for 1-2 minutes.

Strain the liquid, discarding the kombu and bonito flakes. Pour the liquid back into the pot.

Whisk the miso into the broth and add the shiitake mushrooms and tofu.

Simmer over low-medium heat for 3 minutes.

Serve.