01 - Melt the butter with olive oil in a large soup pot over medium heat. Add the chopped onion and cook, stirring occasionally, until softened and translucent, about 3 to 4 minutes.
02 - Add the minced garlic and sliced mushrooms to the pot. Cook for 8 to 10 minutes, stirring occasionally, until the mushrooms are deeply browned and most of their released moisture has evaporated.
03 - Stir in the dried thyme, salt, and black pepper, coating the mushrooms and onions evenly with the seasonings.
04 - Pour in the vegetable broth and bring the mixture to a boil. Once boiling, reduce the heat to low and let the soup simmer gently for 15 minutes to allow the flavors to meld.
05 - For a smoother, creamier texture, use an immersion blender to purée the soup directly in the pot until you reach your preferred consistency. For a rustic version, skip this step or blend only partially.
06 - Stir in the heavy cream and heat gently over low for 2 to 3 minutes. Do not let the soup boil after adding the cream. Taste and adjust the salt and pepper as needed.
07 - Ladle the hot soup into individual bowls and garnish with chopped fresh parsley. Serve immediately with crusty bread or garlic toast on the side.