Start by melting the butter in a large pot over medium heat. Toss in the finely diced onion. Sauté it until it’s translucent, which usually takes about 5 minutes. The butter and onion aroma is just the beginning of a fantastic flavor journey. Once your onions have softened, add the chopped mushrooms. Continue cooking until they release their moisture, about 7-10 minutes. You want the mushrooms to be nicely browned and fragrant.

Sprinkle the flour over the mushroom mixture. Stir well to coat the vegetables evenly. This creates a roux, which will help thicken your soup later. Cook for about 2 minutes, allowing the flour to lose its raw taste. You’ll notice the mixture becoming slightly golden.

Slowly pour in the broth while continuously stirring to prevent any lumps. This will help the roux dissolve into the liquid. Bring this mixture to a gentle simmer. Keep it cooking for about 10 minutes. This allows the flavors to meld and deepens the soup.

Once you’ve achieved a gentle simmer, it’s time to add the heavy whipping cream. Stir well to incorporate. Now for the best part: Add the brie. Stir until it melts and fully combines with the soup. It should become creamy and delightful. Don't forget to add thyme, salt, and pepper at this stage. Adjust these to your taste preference.

If you prefer a smooth soup, you can blend it at this stage using an immersion blender. Alternatively, carefully transfer portions to a regular blender. Blend until silky. However, if you prefer chunks, simply skip this step.

Ladle the soup into bowls, adding croutons and a sprinkle of fresh parsley on top for a pop of color. Grab your crusty bread, and get ready for a warm embrace in a bowl.