Melt butter and olive oil in a large pot over medium heat.
Add sliced onions and cook slowly until deeply caramelized.
Stir in garlic and cook briefly.
Add wine and scrape the pot to release flavor.
Pour in broth, thyme, and bay leaf, then simmer for 20 minutes.
Toast baguette slices until crisp.
Ladle soup into oven-safe bowls and place bread on top.
Sprinkle with Gruyère and Parmesan cheese.
Broil until cheese melts and becomes golden.
Notes
Take time caramelizing onions for the best flavor.
Use good-quality broth for a richer soup base.
Gruyère cheese gives the most authentic taste.
Toast bread well so it holds up under the cheese.
Serve immediately after broiling for best texture.
Timings
Prep Time: 15 minutes
Cook Time: 50 minutes
Total Time: 1 hour 5 minutes
Servings
4 servings
Calories
Approximately 320 calories per serving
Calories 320 kcal
Fat 16 g
Saturated Fat 9 g
Carbohydrates 28 g
Sugar 7 g
Protein 15 g
Sodium 780 mg