Season the beef generously on all sides with Kosher salt and black pepper, then allow to sit out at room temperature.
Heat olive oil over medium-high heat in a large saucepan or pot. When hot, add chopped onion, season with 1 tsp Kosher salt, then cook, stirring occasionally.
Pour in beef broth, bring to a boil, then simmer. Carefully transfer to a blender, then add apple cider vinegar. Blend until smooth, then strain through a fine mesh sieve. Pour the sauce into the Dutch oven, then taste and adjust seasoning.
Carefully remove the beef from the braising liquid, then shred with a couple forks. Discard the bones and any cartilage from the short ribs. Place the shredded beef in a bowl with a ladleful of the braising liquid, then stir.
Dip a corn tortilla into the braising liquid, then carefully add it to the hot pan. Cook. Add a layer of the braised beef to one side of the tortilla, then add a generous sprinkle of shredded cheese on top. Close the tack, then cook until crisp and the cheese has melted.
Serve immediately with a bowl of the braising liquid on the side for dipping. Enjoy with fresh lime wedges, minced onion, and cilantro.