01 -
In a large pot, melt the butter over medium heat. Add the sliced onions and a pinch of salt. Cook, stirring occasionally, for about 30-40 minutes until the onions are deeply caramelized and golden brown. This slow cooking is key to developing the soup's rich flavor.
02 -
Once the onions are caramelized, add the white wine to deglaze the pot, scraping up any browned bits from the bottom. Cook for about 5 minutes until the wine has reduced slightly. Pour in the beef broth, add thyme, bay leaves, and season with salt and pepper. Bring to a simmer and cook for another 15-20 minutes.
03 -
While the soup simmers, preheat your oven to 400°F (200°C). Arrange the baguette slices on a baking sheet. Brush lightly with olive oil if desired. Toast in the oven for about 10 minutes until golden and crispy.
04 -
Remove the bay leaves from the soup. Ladle the soup into oven-safe bowls, topping each with a slice of toasted baguette and a generous amount of shredded Gruyère cheese. Place the bowls on a baking sheet and broil in the oven for about 2-3 minutes, or until the cheese is bubbly and golden.