Follow these clear steps to create your own version of Outback Steakhouse Walkabout Onion Soup:

1. Caramelize the Onions: In a large saucepan, heat the butter and olive oil over medium heat. Add the sliced onions, salt, and sugar. Cook for 30-35 minutes, stirring frequently until the onions are caramelized and golden brown.
2. Add the Broth: Pour in the beef broth, followed by the dry white wine, Worcestershire sauce, black pepper, and garlic powder. Bring the mixture to a boil.
3. Simmer: Reduce the heat and let the soup simmer for 15 minutes, allowing the flavors to meld together.
4. Prepare the Bread: While the soup simmers, preheat your oven to 350°F (175°C). Toast the slices of French baguette until golden brown.
5. Assemble the Soup: Pour the hot soup into oven-safe bowls. Place a slice of toasted baguette on top of each bowl.
6. Top with Cheese: Generously sprinkle the shredded mozzarella and provolone cheese over the baguette.
7. Broil: Place the bowls onto a baking sheet and broil in the oven for about 3-5 minutes, or until the cheese is bubbly and golden.
8. Serve: Carefully remove from the oven and allow to cool slightly before serving.

Each step in this process builds upon the last, ensuring that you create a soup that is as flavorful as it is hearty.