Heat the olive oil and butter in a large pot over medium heat.
Add the onion, salt, and several grinds of pepper and cook for 2 minutes, or until softened slightly.
Add half the mushrooms and cook, stirring occasionally, for 5 minutes, or until softened.
Add the remaining mushrooms and cook for another 5 minutes.
Add the cornstarch, mix it in.
Stir in the garlic, followed by the wine, broth, tamari, and thyme.
Cover and simmer for 15 minutes.
Allow the soup to cool slightly, then transfer two-thirds to a blender and blend until smooth.
Stir the blended soup back into the pot with the chunky soup.
If desired, add the cream and cook for another 2 minutes, or until the soup is warmed through and the raw cream taste has cooked off.
Season to taste.
Ladle into bowls and serve topped with a drizzle of olive oil and/or cream, fresh parsley, and thyme.
