01 - Heat olive oil and butter in a large pot over medium heat. Add chopped onion, diced carrot, and celery; cook for 5 minutes until softened.
02 - Incorporate minced garlic and cook for 1 minute until fragrant.
03 - Add sliced mushrooms and sauté for 8 to 10 minutes, stirring occasionally, until browned and moisture evaporates.
04 - Pour in 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. Blend soup using an immersion blender or in batches with a regular blender until smooth or desired consistency.
07 - Stir in heavy cream and warm gently for 2 to 3 minutes. Adjust seasoning as needed.
08 - Ladle soup into bowls and garnish with fresh thyme leaves. Serve hot.