Preheat oven to 275°F (135°C). Line a large baking sheet with heavy-duty aluminum foil.
Remove the thin membrane from the back of the beef ribs if still attached.
In a small bowl, mix the brown sugar, smoked paprika, garlic powder, onion powder, salt, black pepper, and cayenne pepper to create the dry rub.
Generously apply the dry rub all over both sides of the ribs, pressing firmly so it adheres.
Place the ribs meat-side up on the prepared baking sheet. Cover tightly with another piece of foil to trap the steam.
Bake for 2.5 to 3 hours, or until the meat is very tender and pulling away from the bone.
In a small bowl, whisk together the barbecue sauce and apple cider vinegar.
Remove the ribs from the oven and discard the top layer of foil. Increase oven temperature to 400°F (200°C).
Brush the ribs generously with the barbecue sauce mixture.
Return the ribs to the oven, uncovered, for 10-15 minutes until the sauce is sticky and caramelized.