Making the Best French Onion Soup requires some attention, but it’s fairly simple. Just follow these steps to achieve a perfect bowl:

1. Melt Butter and Oil: In a large pot, melt the butter and olive oil over medium heat.
2. Add Onions: Add the sliced onions and salt to the pot. Stir well to coat the onions in the butter.
3. Caramelize the Onions: Reduce the heat to low and cook the onions, stirring occasionally, for about 30-40 minutes until they turn golden brown and caramelized.
4. Add Sugar and Flour: Sprinkle the sugar and flour over the onions. Stir well and cook for an additional 5-10 minutes.
5. Deglaze with Wine: Gradually pour in the white wine (if using) while scraping the bottom of the pot. Allow it to simmer for 5 minutes.
6. Add Broth and Seasonings: Pour in the beef broth, thyme, and black pepper. Bring to a gentle boil, then reduce the heat and let it simmer for at least 30 minutes.
7. Preheat the Broiler: While the soup simmers, preheat your broiler to high.
8. Prepare the Bread: Arrange the baguette slices on a baking sheet. Toast them under the broiler until golden and crispy, about 2-3 minutes per side.
9. Serve the Soup: Ladle the soup into oven-safe bowls, topping each with a slice of toasted baguette.
10. Add Cheese: Generously sprinkle Gruyère cheese and Parmesan cheese on top of the bread.
11. Broil: Place the bowls under the broiler for about 3-5 minutes, or until the cheese is bubbling and golden brown. Watch carefully to prevent burning.
12. Garnish: Serve hot, garnished with a sprinkle of additional thyme if desired.

These straightforward steps will lead you to create the Best French Onion Soup that is sure to impress anyone you serve it to.