In a large pot or Dutch oven, heat the olive oil over medium-high heat.

Season the short ribs with salt and pepper, then brown them on all sides, about 3-4 minutes per side. Remove the ribs and set aside.

In the same pot, add the sliced onions and cook, stirring frequently, until they are caramelized and golden brown, about 15-20 minutes.

Add the minced garlic and thyme, cooking for an additional minute until fragrant.

Return the short ribs to the pot, then pour in the beef broth, red wine, and Worcestershire sauce.

Bring the mixture to a boil, then reduce the heat to low and cover. Simmer for 2-3 hours, or until the meat is tender and falls off the bone.

Once the soup is ready, preheat your oven to 350°F.

Place the baguette slices on a baking sheet and toast them in the oven for about 5-7 minutes until golden brown.

To serve, ladle the soup into bowls, top each bowl with a slice of toasted baguette, and sprinkle with shredded Gruyère cheese.

Place the bowls under the broiler for 2-3 minutes until the cheese is melted and bubbly.