In a small bowl mix together the paprika, salt, thyme, garlic powder, onion powder, black pepper and cayenne pepper. Remove the membranes from the bone side of all of the racks of ribs using a sharp knife and peeling the membrane off. Rub the seasoning all over the ribs. Place the ribs in a container or a bowl, loosely covered, and refrigerate for 4 to 24 hours.
Before you’re ready to cook the ribs, make the basting sauce. In a medium saucepan combine the garlic, scallions, ketchup, molasses, butter, vinegar, mustard, or hot sauce and stir over medium heat until the butter is melted. Let simmer for another 15 minutes or so. You can make this ahead of time and reheat.
Preheat the oven to 350°F. Line two rimmed baking sheets with aluminum foil. Place the ribs bone side down in a roasting pan and pour 1 cup of water into each pan. Roast until the meat starts to pull away from the bones, about 1 1/2 hours.
Remove the pans from the oven and drain off any remaining water. Baste the ribs generously with the sauce. Baste them on all sides with the sauce and bake for another 1/2 hour in the oven, bone side down. You can put them under the broiler for the last 2 minutes or so to give them a nicely caramelized top (watch them carefully so they don’t burn!).
Let the rib racks sit for 10 minutes before cutting them into individual ribs and serving.