In a large pot, melt the butter over medium heat.

Add the onion and garlic, and sauté until soft and translucent.

Add the mushrooms and cook until they release their moisture and start to brown.

Sprinkle the flour over the mushrooms and stir well to combine.

Gradually add the broth, stirring constantly to avoid lumps. Bring to a simmer and cook for about 10 minutes.

Stir in the heavy cream and simmer for another 5 minutes.

Use an immersion blender to blend the soup until smooth, or leave it chunky if preferred.

Season with salt and pepper to taste.

Serve hot, garnished with fresh parsley if desired.