Preheat oven to 350°F. Season ribs with salt and pepper. Heat oil in a Dutch oven or large ovenproof pot over medium-high. Working in batches if necessary, sear ribs until browned on all sides, 8–10 minutes. Transfer ribs to a plate.
Drain fat from pot. Add prune juice, teriyaki sauce, and 1 1/2 cups water. Bring to a simmer and return ribs to pot. Cover pot, transfer to oven, and braise until beef is very tender and falling off the bone, 2–3 hours.
Transfer ribs to a platter. Bring liquid in pot to a boil on stovetop. Cook, uncovered, until liquid is reduced to a glaze, 12–15 minutes. Season with salt and pepper; pour over ribs.
- 3 pounds bone-in beef short ribs
- Kosher salt, freshly ground black pepper
- 2 tablespoons olive oil
- 1 cup prune juice
- 1 cup teriyaki sauce