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.
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.
