01 - Melt butter in a large pot over medium heat. Add onions and celery, sautéing for 3 to 4 minutes until softened.
02 - Incorporate minced garlic and cook for 1 minute until fragrant.
03 - Add sliced mushrooms and cook for 8 to 10 minutes, stirring occasionally, until the liquid evaporates mostly and mushrooms turn golden.
04 - Pour in dry white wine, if using, and let it simmer for 2 minutes.
05 - Add vegetable stock, fresh thyme leaves, and bay leaf. Bring to a gentle boil, then reduce heat and let simmer for 15 minutes.
06 - Remove bay leaf. Use an immersion blender to blend the soup until smooth or slightly textured according to preference.
07 - Stir in heavy cream and season with salt and pepper. Heat gently for 2 to 3 minutes, avoiding boiling.
08 - Ladle soup into bowls, garnish with a drizzle of cream and sprigs of fresh thyme, and serve immediately.