01 - Heat butter and olive oil in a large pot over medium heat.
02 - Add onions, carrot, and celery; sauté for 5 minutes until softened.
03 - Stir in minced garlic and cook for 1 minute until fragrant.
04 - Add mushrooms and sauté for 8 to 10 minutes until they release juices and start to brown, stirring occasionally.
05 - Pour in dry white wine if using, and cook for 2 minutes until mostly evaporated.
06 - Add fresh thyme leaves, bay leaf, salt, and black pepper; stir to combine.
07 - Pour in vegetable broth, bring to a simmer, cover, and cook for 15 minutes.
08 - Remove bay leaf, then use an immersion blender or transfer in batches to a countertop blender; blend until smooth and return to pot.
09 - Stir in heavy cream and gently heat until warmed through; adjust seasoning to taste.
10 - Ladle hot soup into bowls, garnish with extra thyme and a drizzle of cream if desired; serve alongside crusty bread.