Saut in large pot mushrooms, onions and celery with olive oil until mushrooms have released most of their moisture and liquid has reduced to a minimal amount. Add garlic and stir for a minute.
Add vegetable broth and bring to boil, turn down heat and add thyme sprigs. Cover and simmer for 20-30 mins.
Take out thyme sprigs. Turn up heat again until soup starts boiling. Make cornstarch slurry by adding cornstarch to cold water in separate small bowl. And add slowly to bubbling soup while stirring. Adding just enough for soup to thicken and turn clear. Turn off heat.
Make miso paste slurry and add when soup is no longer bubbling. Stir to combine. Do not boil the soup again after miso has been added.
Add only the solid part of the can of coconut milk. Stirring until the cream has melted and is fully incorporated. Adjust salt and pepper seasonings. Garnish with parsley.
