Cook the soup
In a large, heavy saucepan over medium heat, melt the butter. Add the shallot and sauté until translucent, about 2 minutes. Add the mushrooms, cover, and cook until their juices are released, about 3 minutes. Stir in the flour and cook, stirring, until thoroughly blended, about 1 minute. Pour in the broth and brandy. Bring to a boil, cover, reduce the heat to medium, and simmer for 15–20 minutes.