Season the ribs with a generous amount of salt and pepper. Place the ribs, meat side up, in a large roasting pan or rimmed baking sheet.
Cover with aluminum foil, then bake until the meat falls easily from the bones, 2 ½ hours.
While the ribs are cooking, prepare the barbecue sauce. Heat the olive oil in a saucepan over medium heat, add the onions and cook until tender and translucent, 5 to 8 minutes. Stir in the cumin and garlic and cook for 30 seconds. Add the remaining ingredients. Stir and cook for 2 minutes.
Remove ribs from oven, discard foil and generously brush both sides with barbecue sauce.
Move oven rack near the top of the oven. Broil ribs on high for 3-4 minutes, just until the sauce begins to caramelize. Keep a close eye on the ribs so the sauce does not burn.
