In a large pot, heat the olive oil over medium-high heat. Season the beef short ribs with salt and pepper. Add them to the pot and brown on all sides, about 3-4 minutes per side. Remove and set aside.

In the same pot, lower the heat to medium and add the butter. Add the sliced onions, cook slowly, stirring occasionally, until they are caramelized, about 20-25 minutes.

Once the onions are caramelized, add the minced garlic and cook for an additional minute. Pour in the red wine, scraping the bottom of the pot to release the flavors. Allow it to reduce for about 5 minutes.

Return the short ribs to the pot, add the beef stock, thyme, and bay leaf. Bring to a simmer, cover, and cook for 1.5 hours, or until the beef is tender.

Preheat your broiler. Ladle the soup into oven-safe bowls, top each with a slice of toasted baguette, and generously sprinkle with gruyère cheese. Place under the broiler for 2-3 minutes until the cheese is bubbly and golden.

Allow the soup to cool slightly before enjoying the cheesy, savory goodness!