In a large heavy pot or Dutch oven, heat about 2 tablespoons of oil over medium-high heat. Once the oil shimmers, add the beef short ribs, ensuring they don’t overcrowd the pot. Sear them on all sides until they develop a deep brown crust, about 5–7 minutes.

Remove the seared short ribs from the pot and set them aside on a plate. In the same pot, add the sliced onions, stirring frequently to coat them in the flavorful drippings. Cook over medium heat until they turn golden and soft, approximately 20–25 minutes.

Once the onions are perfectly caramelized, return the short ribs to the pot. Pour in about 6 cups of beef broth along with the fresh thyme and balsamic vinegar. Stir well and bring the mixture to a gentle boil. Then, reduce the heat to low, cover the pot, and let it simmer for about 1 hour.

After simmering, carefully remove the short ribs from the pot and set them on a cutting board. Let them cool slightly, then use two forks to shred the tender meat, discarding the bones. Return the shredded beef into the pot and stir it into the broth.

Ladle the rich soup into individual bowls, ensuring each has a generous portion of shredded beef and caramelized onions. Top each bowl with a mound of shredded Gruyère cheese. Place the bowls under the broiler in your oven for about 5 minutes, or until the cheese is bubbly and slightly browned.

Gather around the table and serve your French Onion Beef Short Rib Soup warm, accompanied by crusty bread or crackers.