Caramelize the Onions:
In a large Dutch oven or pot, melt olive oil and butter over medium heat. Add the onions and salt, stirring to coat them with butter. Cook, stirring occasionally, until the onions are golden and caramelized, about 30-40 minutes. Stir every 10-15 minutes to ensure even cooking, reducing the heat if the onions darken too much.

Add Flour and Garlic:
Once the onions are caramelized, add the flour and minced garlic. Stir to coat the onions, and cook for another 2 minutes.

Deglaze the Pan and Simmer:
Add the white wine (or beef broth) to deglaze the pan, scraping up any brown bits from the bottom. Then, add the beef broth, thyme, black pepper, Worcestershire sauce, and bay leaf. Simmer uncovered for 30 minutes.

Taste and Adjust Seasonings:
After 30 minutes, remove the bay leaf and taste the soup. Add more salt or pepper if needed.

Prepare the Toasted Baguette:
About 10 minutes before the soup is done, preheat the oven to 400°F (200°C). Line a large baking sheet with parchment paper, then arrange the baguette slices in a single layer. Brush one side with butter and sprinkle with garlic powder. Toast in the oven for 5 minutes per side, or until golden brown.

Finish the Soup:

Option 1: Sprinkle shredded cheese on top of the toasted baguette slices and bake for an additional 3-5 minutes until the cheese is melted. Ladle the soup into bowls and add a slice or two of the cheesy baguette on top. Serve immediately.

Option 2: Alternatively, ladle soup into oven-safe bowls or crocks, place a toasted baguette slice on top, and sprinkle with 1/3 cup of shredded Gruyère. Broil for about 2 minutes until the cheese is melted and bubbly. Serve immediately.