To make the dashi, cut the kombu and rinse well. Then soak kombu (and shiitake mushrooms if you have them) in 7 cups water in a large pot for at least an hour, but I recommend overnight. The next day, set pot over medium heat and bring the mixture to a boil. Remove kombu just before it beings to boil (or else it will taste bitter). Simmer for about 5 minutes after the kombu is removed, then turn off the heat.

Strain using a coffee filter over a sieve, then transfer back to pot. If eating immediately, in a separate bowl, whisk miso paste (1 tbsp per 1 cup broth) for however many servings you are making in about 1/2 cup hot dashi (this recipe makes about 6 servings).

Ladle 1 cup dashi per serving, and add adequate amount of dissolved miso. Add tofu, sliced green onion, wakame seaweed and serve immediately.