Ingredients
Method
- Place the sliced onions in the slow cooker. Pour the melted butter and brown sugar over them and toss to coat.
- Cover and cook on low for 8 hours to deeply caramelize the onions.
- Pour in the beef broth and thyme, and cook for 1 more hour on high.
- Ladle the soup into oven-safe bowls, top each with a slice of toasted French bread and a handful of Gruyere cheese.
- Broil in the oven for 2 minutes until the cheese is bubbly and golden.