01 - Heat butter and olive oil in a large pot over medium heat until melted and shimmering.
02 - Add chopped onions, diced carrot, and celery; sauté for 5 minutes until softened.
03 - Stir in minced garlic and cook for 1 minute until fragrant.
04 - Incorporate sliced mushrooms and cook, stirring occasionally, for 8 to 10 minutes until they release their moisture and start to brown.
05 - Pour in white wine, if using, and simmer for 2 minutes until mostly evaporated.
06 - Add thyme leaves, bay leaf, salt, and black pepper; stir to combine.
07 - Pour in vegetable broth, bring to a simmer, cover, and cook gently for 15 minutes to develop flavor.
08 - Remove the bay leaf. Blend soup using an immersion blender until smooth, or blend in batches in a countertop blender and return to the pot.
09 - Stir in heavy cream and warm the soup gently until heated through. Adjust seasoning to taste.
10 - Ladle hot soup into bowls. Garnish with extra thyme and a drizzle of cream if desired. Serve with crusty bread on the side.