Preheat your oven to 300°F (150°C). Season the short ribs with salt and black pepper.

In a large oven-safe pot or Dutch oven, heat the vegetable oil over medium-high heat. Sear the short ribs on all sides until browned, about 3-4 minutes per side. Remove the short ribs and set aside.

In the same pot, add the chopped onion, garlic, and ginger. Sauté until the onion is translucent, about 5 minutes.

Add the beef broth, soy sauce, brown sugar, rice vinegar, sesame oil, and five-spice powder to the pot. Stir well to combine.

Return the short ribs to the pot, ensuring they are submerged in the liquid. Cover the pot with a lid and transfer it to the preheated oven. Cook for 3 hours, or until the meat is tender and easily falls off the bone.

Once cooked, remove the pot from the oven and let the short ribs cool slightly. Shred the meat using two forks, discarding any bones and excess fat.

While the meat is cooling, steam the bao buns according to package instructions or until fluffy and warm.

To assemble, place a generous amount of shredded short rib in each bao bun. Top with sliced green onions and cilantro leaves.