Preheat the oven to 275 degrees F.
For the rub: Whisk together the paprika, salt, sugar, garlic powder, onion powder, black pepper, mustard and cayenne for the rub. Turn the rib racks bone-side-up and remove the thin membrane layer covering the ribs by lifting up a small corner with a paring knife and tugging it off. You can use a paper towel to secure your grip. Rub the spice mixture all over both racks. Place both racks, bone-side-up, on a baking sheet lined with foil. Cover with foil and put in the oven. The meat should be tender enough to easily insert your knife into the ribs after 1 1/2 hours.
As the ribs cook, make your BBQ sauce. Heat the oil in a medium saucepan over medium heat. Stir in the garlic, tomato paste, chili powder, paprika, red pepper, allspice and cloves and cook, stirring, until the paste is dark brick red, about 3 minutes. Add the ketchup, 2 cups water, vinegar, molasses, brown sugar, salt, soy sauce, Worcestershire, mustard, black pepper and bay leaf. Adjust the heat to maintain a gentle simmer and cook until the flavors come together, about 30 minutes. Remove and discard bay leaf before using. You should have about a quart of sauce. Set aside 1 1/2 cups of sauce for basting. Serve the remaining sauce on the side for dipping.
After the ribs have been in the oven for 1 1/2 hours, remove the foil cover and brush the ribs with BBQ sauce. Cook uncovered until the meat is fork tender and comes off the bone easily, another 1 1/2 hours. While the ribs cook, keep basting and flipping them every half hour. Serve with reserved BBQ sauce on the side. Keep any leftover BBQ sauce in your refrigerator for up to 2 weeks.