For the ribs: Preheat the oven to 275 degrees F. Line a baking sheet with foil, enough to fold over the ribs, approximately twice the size of the baking sheet.
In a small mixing bowl, combine the sugar, paprika, salt, chile powder, cumin, garlic powder and cinnamon. Reserve 1 tablespoon of the rub and set aside.
Place the ribs on the prepared baking sheet. Generously sprinkle the ribs on both sides with the spice mixture. Really rub it in! Place the ribs meat-side down and fold the foil tightly around the ribs to make a sealed packet. Bake the ribs until they become pliable but not falling apart, 2 to 2 1/2 hours. You know the ribs are done when the meat pulls away from the bone. Once the ribs are tender, carefully pour off 1/2 cup of the accumulated juices into a bowl and reserve. Keep the ribs wrapped in the foil to keep warm.
For the sauce: In a small saucepan, combine the tomato puree, molasses, vinegar, worcestershire sauce, reserved rub and the garlic. Add 1/2 cup of the reserved cooking juices and bring the sauce to a boil. Reduce the heat and simmer until the sauce thickens and coats the back of a spoon, about 10 minutes.
Preheat a grill pan over high heat. Just before serving, slather the ribs with the tangy bbq sauce and char them on the grill pan, basting them with the sauce and turning as they char up. If you don't have a grill pan, you can slather them with sauce and stick them under the broiler to char. Serve the ribs with extra BBQ sauce on the side.