In a large pot or Dutch oven, heat the olive oil over medium-high heat. Season the short ribs with salt and pepper, then sear them in the pot until browned on all sides. Remove the short ribs and set aside.

In the same pot, add the sliced onions and cook over medium heat, stirring frequently, until they are caramelized, about 25-30 minutes. Add the minced garlic, sugar, thyme, and bay leaf, cooking for an additional 2 minutes.

Pour in the red wine, scraping the bottom of the pot to deglaze. Let it simmer for about 5 minutes until slightly reduced.

Return the short ribs to the pot, then add the beef broth and Worcestershire sauce. Bring to a boil, then reduce the heat to low and cover. Simmer for 2-3 hours, or until the meat is tender and falling off the bone.

Preheat the oven to 400°F. Arrange the baguette slices on a baking sheet and toast them in the oven for about 5-7 minutes until golden brown.

Once the soup is ready, remove the short ribs and shred the meat, discarding the bones. Return the shredded meat to the pot and stir to combine.

To serve, ladle the soup into bowls, top with toasted baguette slices, and sprinkle generously with shredded Gruyère cheese. Place under the broiler for 2-3 minutes until the cheese is bubbly and golden.