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

2. In the same pot, reduce heat to medium. Add butter and sliced onions. Cook slowly, stirring often, until deeply golden and caramelized (about 40 minutes). Add garlic in the final 2–3 minutes.

3. Pour in red wine, scraping up browned bits. Let reduce for 5 minutes. Add short ribs back in, along with beef stock and thyme. Bring to a boil, then simmer covered for 2.5 to 3 hours until meat is fork-tender.

4. Remove short ribs, discard bones if necessary, and shred meat. Return shredded beef to the pot. Adjust salt and pepper to taste.

5. Toast baguette slices. Ladle soup into oven-safe bowls, top each with toasted bread, and cover generously with shredded Gruyère.

6. Broil until cheese is bubbly and golden brown. Serve hot.