01 - Heat olive oil and butter in a large pot over medium heat. Add onion, carrot, and celery; cook for 5 minutes until softened.
02 - Stir in minced garlic and cook for 1 minute until fragrant.
03 - Add sliced mushrooms and cook for 8 to 10 minutes, stirring occasionally, until browned and excess moisture has evaporated.
04 - Pour in dry white wine, if using, and simmer for 2 to 3 minutes until mostly reduced.
05 - Add vegetable broth, fresh thyme, bay leaf, salt, and pepper. Bring to a boil, then reduce heat and simmer uncovered for 15 minutes.
06 - Remove bay leaf. Use an immersion blender or work in batches with a blender to puree the soup to desired smoothness.
07 - Stir in heavy cream and heat gently for 2 to 3 minutes. Adjust seasoning as needed.
08 - Ladle the soup into bowls and garnish with fresh thyme leaves. Serve immediately.