Heat 2 tablespoons of butter and olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add half of the chopped mushrooms and sauté until deeply browned and most of their moisture has evaporated (about 8-10 minutes). Remove browned mushrooms and set aside.

Reduce heat to medium. Add the remaining 2 tablespoons of butter to the pot. Add the diced shallot and sauté until translucent, about 3 minutes. Add the minced garlic and fresh thyme, cooking for 1 minute until fragrant, being careful not to burn the garlic.

Stir in the remaining raw mushrooms with the aromatics. Cook until these mushrooms have released their liquid and begun to brown slightly (about 5 minutes). Sprinkle the flour over the mixture and stir continuously for 1 minute to cook out the raw flour taste.

Deglaze the pot by pouring in the white wine, scraping up any browned bits from the bottom. Let the wine simmer and reduce by half (about 2-3 minutes).

Pour in the broth. Bring the mixture to a simmer, then allow it to cook gently for 10 minutes, allowing the flavors to meld.

Carefully transfer the soup mixture (including the reserved browned mushrooms) to a blender, or use an immersion blender directly in the pot. Blend until mostly smooth, leaving some texture if desired. Return the soup to the pot if necessary.

Stir in the heavy cream, salt, and pepper. Heat gently until warmed through, but do not allow the soup to boil after adding the cream. Taste and adjust seasoning as needed. Serve hot, garnished with fresh parsley or a drizzle of truffle oil (optional).