1. In a large skillet, brown the mushrooms over high heat in butter. Season with salt and pepper.
 
2. Place the cooked mushrooms in a bowl.
 
3. In a large saucepan, brown the onions and garlic in the remaining butter. Add the flour and cook for 1 minute, stirring. Add the broth, thyme, and reserved mushrooms. Season with salt and pepper. Bring to a boil and simmer over low heat for about 15 minutes.
 
4. Remove the thyme sprig and blend the mixture into a very smooth purée. Adjust the seasoning.
 
5. Pour the soup into bowls. Garnish with sautéed mushrooms. Decorate with a Roman petal cheese spiral. Season with pepper and serve.