In a small bowl, combine the very hot water and dried shiitake mushrooms. Allow to soak for about 20-30 minutes and retain the soaking liquid. If you have fresh shiitake mushrooms, slice and combine with the brown/white mushrooms. Omit water and add 2 additional cups of broth in place of soaking liquid.

In a large soup pot, melt the butter over medium-low heat. Add the onion and sauté about 3-5 minutes, until browned. Now, add the brown/white mushrooms and sauté for about 10 minutes until all their water has evaporated and they are shrunken and fragrant.

Add the sage and the flour to the mushrooms. Stir to coat and cook for a minute or two.

Now, add the broth, soy sauce, Worcestershire sauce, and the reconstituted dried shiitakes as well as the soaking liquid. Bring to a boil then cover. Turn down to low and simmer for about 15 minutes.

Add the coconut milk, vinegar, agave nectar, and nutritional yeast. Stir to combine over low heat.

In a small bowl, whisk the cornstarch into the cold water. Then, pour slowly into the soup while whisking. Continue to whisk for a few minutes, until the soup thickens slightly. Remove from heat and stir in parsley.

Serve hot.