Prepare the onions by peeling and slicing them thinly into even rings.

In a large skillet, melt the butter over medium heat, then add the olive oil. Once heated, add the sliced onions, salt, pepper, and sugar, and cook for about 10-15 minutes until the onions are caramelized and golden brown, stirring frequently to prevent burning.

Transfer the caramelized onions to the slow cooker.

Add the halal beef broth, halal chicken broth, Worcestershire sauce, bay leaf, and dried thyme to the slow cooker. Stir gently to combine.

Cover the slow cooker with the lid and cook on low heat for 6-8 hours or on high heat for 3-4 hours. Remove the bay leaf before serving.

While the soup is finishing cooking, preheat your oven to 375°F (190°C). Place the baguette slices on a baking sheet and toast them in the oven for 8-10 minutes or until lightly golden and crisp.

Once the baguette slices are toasted, sprinkle shredded Gruyère cheese generously on top of each slice. Return them to the oven and bake for an additional 5 minutes, or until the cheese is melted and bubbling.

Ladle the soup into bowls and top each bowl with a cheesy baguette slice. Serve warm and enjoy!