Remove ribs from refrigerator 30-45 minutes before cooking. Pat completely dry with paper towels, peel off any thick membrane on the bone side, and rub olive oil all over the meat.
In a small bowl, combine brown sugar, paprika, garlic powder, onion powder, chili powder, kosher salt, black pepper, cumin, and smoked paprika (if using). Whisk until no clumps remain.
Generously coat all sides of each rib with the spice rub, pressing into the meat. For deeper flavor, refrigerate covered for 2-4 hours or overnight.
Preheat oven to 300°F (150°C). Line a roasting pan with heavy-duty foil, leaving overhang for sealing. Arrange ribs bone-side down in a single snug layer.
Cover ribs tightly with a second sheet of foil, crimping edges to create a sealed packet. Bake for 3 to 3.5 hours until meat pulls away from the bone and a fork slides in easily.
Carefully remove from oven and peel back foil, watching for steam. Tilt pan and spoon off excess fat and liquid to prevent grease fires during broiling.
Switch oven to broil and position rack 6 inches from heat. Brush ribs generously with BBQ sauce and broil 3-5 minutes until sauce bubbles and caramelizes. Apply a second coat and broil 2-3 minutes more for extra glaze.
Remove ribs from oven and let rest 5-10 minutes before serving. Transfer to a platter and pour any remaining pan juices over the top.