First clean the kombu by wiping it down gently with a damp cloth, do not rinse it. Cut a few slits around the edges of the kombu. (see below)
To make hot dashi
Place 5 cups of filtered water, kombu and shiitake into a medium-sized saucepan. Bring to a small simmer over medium heat (do not boil) for 20 minutes. Lower the heat a bit as needed if it starts to boil. Skim any froth off the top of the water with a skimmer. Remove the kombu and shiitake before serving. (You can reserve the shiitake for making stock later or slice it up and put it into the miso soup.)
To make cold dashi
Place 4 cups of filtered water, kombu and shiitake into a container, cover and allow to sit 12 hours in the refrigerator. Remove the kombu and shiitake before serving.
To prepare the miso soup
Ladle the vegan dashi into bowls. If using cold dashi, gently heat it on the stovetop first. Season with the miso, soy sauce and toasted sesame oil, adding any extra components as desired.
Recipe by Olives for Dinner at https://olivesfordinner.com/2015/04/easy-miso-soup.html