1. In a large pot over medium heat, melt the butter with olive oil. Add the sliced onions and cook, stirring occasionally, until they begin to soften, about 10 minutes.
2. Reduce the heat to low, add the sugar, and continue to cook the onions until they are deeply caramelized, stirring frequently for about 30-35 minutes. This step requires patience, but the reward is golden and flavorful onions.
3. Stir in the minced garlic and cook for another minute until fragrant.
4. Add the white wine to deglaze the pot, scraping up any brown bits from the bottom. Let it simmer for 2-3 minutes until reduced by half.
5. Pour in the beef broth and add the thyme. Season with salt and pepper to taste. Bring the soup to a simmer and let it cook for 20 minutes, allowing the flavors to meld together.
6. Preheat your oven’s broiler. Ladle the soup into oven-safe bowls, place a slice of toasted baguette on top of each, and generously sprinkle with Gruyère cheese.
7. Place the bowls on a baking sheet and broil in the oven until the cheese is bubbly and golden brown, about 3-5 minutes. Keep a close eye to prevent burning.

Each step is a tribute to the lessons I’ve learned in my kitchen: patience, attention to detail, and the joy of creating something delicious from scratch.