Bistro French Onion Soup with Croutons

Add sliced onions, butter, olive oil, and salt to a medium heavy-bottomed pot or Dutch oven.
Over medium heat, cook the onions for 30-40 minutes, or until deeply caramelized. You'll have to stir them often, especially after the first 20 minutes. You may need to add a tablespoon or two of water to keep them from sticking or burning. Turn heat to medium-low if they start to cook too quickly.
Once the onions are caramelized, deglaze the pot with the wine. Scrape with your wooden spoon to get all of the brown bits dissolved.
Add in beef broth, pepper, and thyme sprigs. Bring the soup to a boil, then reduce the heat to maintain a simmer. Cover the pot and simmer for 15-30 minutes.
When the soup is almost ready, heat the broiler and dice your baguette. Broil the cubes slices on a sheet pan until golden on all sides.
Ladle soup into broiler-proof bowls or ramekins placed on the sheet pan. Divide the toasted croutons evenly over the bowls. Divide the cheese over the top of the bread, covering the bread well with the cheese.
Broil until the cheese is bubbling and golden. Serve immediately, being careful with the hot bowls!