Heat 2 tablespoons of olive oil (and 1 tablespoon of butter, if using) in a large pot over medium heat. Add 1 chopped onion or shallot with a pinch of salt. Sauté for about 5 minutes until translucent.

Add 12 ounces of chopped fresh mushrooms to the pot. Stir well and sauté for 7-10 minutes until the mushrooms brown and release moisture.

Add 3 minced garlic cloves and 1 teaspoon of fresh thyme leaves. Cook for an additional minute until fragrant.

Pour in 0.5 cup of white wine (if using) and let it simmer for about 3 minutes to deglaze.

Add 4 cups of vegetable broth, 2 tablespoons of tamari (or soy sauce), 1 teaspoon of salt, and pepper to taste. Bring to a simmer and cook for 10-15 minutes.

Using an immersion blender, carefully puree part of the soup until you reach the desired consistency.

If desired, stir in 1 cup of heavy cream or crème fraîche just before serving. Heat through for about 2 minutes.

Taste and adjust seasoning if needed. Serve in bowls, garnished if desired.