In a large pot or Dutch oven, heat the olive oil and butter over medium-high heat. Once hot, add your short ribs and sear them on all sides until beautifully brown, about 10 minutes. Remove the ribs and set them aside.

In the same pot, add your sliced onions. Stir frequently for about 20-25 minutes until they are caramelized to a lovely golden brown.

Once your onions are caramelized, stir in the garlic and cook for an additional minute. Then, pour in the dry white wine, scraping the bottom of the pot to release all the tasty bits. Next, add the beef broth, thyme, bay leaf, salt, and pepper.

Return the short ribs to the pot. Bring everything to a gentle boil, then reduce the heat to low. Cover the pot and let it simmer for about 2-3 hours.

While the soup simmers, toast your baguette slices until they are golden brown. When you're ready to serve, ladle the soup into bowls, top with a slice of toasted baguette, and add a generous handful of Gruyère cheese.

If you're feeling fancy, place the bowls under a broiler until the cheese is bubbly and golden. Keep an eye on them to avoid burning.