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