Preheat the oven to 325°F and line a sheet pan with aluminum foil.
Combine the granulated garlic, granulated onion, chili powder, paprika, cayenne pepper, cumin, salt, and black pepper in a small bowl.
Pat the ribs dry with paper towels. Remove the membrane from the bone side if necessary.
Season both sides of the ribs with the dry rub, working the seasoning evenly into the meat.
Place the ribs, meat side up, on a large sheet of foil. Fold the foil around the rack, sealing the edges to create a tightly wrapped packet.
Place the packet on the prepared sheet pan and bake at 325°F for approximately 2 hours. Check for tenderness. If necessary, reseal and bake for an additional 15–30 minutes.
Remove the ribs from the oven and let rest for 10 minutes. Carefully open the foil packet and reserve the cooking juices.
Brush the ribs generously with barbecue sauce. Place under the low broiler for approximately 5 minutes.
Remove the ribs, apply a second layer of barbecue sauce, and broil for approximately 5 more minutes, until the sauce is caramelized and sticky. Keep the ribs at least 6 inches from the heating element and watch carefully to prevent burning.
Cut between the bones to separate the ribs. Drizzle with reserved cooking juices and serve.