Ingredients
Method
- Melt the butter in a large pot over medium-low heat.
- Add the sliced onions and cook slowly for 25 minutes until they are deep brown and caramelized.
- Add the mushrooms and cook for 5 more minutes.
- Pour in the beef broth, bring to a simmer, and cook for 10 minutes.
- Ladle the soup into oven-safe bowls. Top each bowl with a slice of baguette and a handful of gruyere cheese.
- Broil in the oven for 2 to 3 minutes until the cheese is melted and bubbly.