Prepare the ribs: Place 1 rib rack, meat side down, on a work surface. With a knife, cut a small slit through the silvery membrane at 1 end of the rack. Using a paper towel, grip the cut portion of the membrane, gently peel it from the rack, and discard. Repeat with remaining rack.
Make the rub: Combine sugar, salt, pepper, paprika, mustard powder, and celery seed in a bowl. (If mixture is clumpy, pass through a medium sieve.) Rub mixture on both sides of each rack. Place ribs on a rimmed baking sheet, cover, and refrigerate for at least 2 hours (or overnight). Let stand at room temperature for 30 minutes before cooking.
Make the sauce: Heat oil in a medium saucepan over medium heat. Add onion and garlic, and cook until onion is tender, 2 to 3 minutes. Add red-pepper flakes and tomato paste, and cook for 1 minute. Stir in bourbon, scraping the pan. Stir in tomatoes, vinegar, Worcestershire sauce, water, and sugar, and cook, continuing to stir, until sugar dissolves.
Simmer the sauce: Bring the sauce to a boil. Reduce heat, and simmer until reduced by 1/3, about 30 minutes. Season with salt and pepper. Let cool slightly. Puree in a blender until smooth. (You should have about 2 cups.) Use immediately, or let cool completely, cover, and refrigerate for up to 2 weeks.
Grill the ribs: If using a gas grill, heat to medium-low. Let ribs stand at room temperature for 30 minutes before cooking. Fold a paper towel into a thick rectangle, and dip it in oil. Hold towel with tongs, and brush oil on top grill rack. Place both rib racks, bone side down, on top grill rack, directly over pan. Cover, keeping top grill vents halfway open and bottom vents completely open to maintain grill temperature of 275 degrees to 325 degrees. Cook ribs, without turning, until the meat is tender but not falling off bones, and has shrunk 1/2 inch from ends, 3 to 3 1/2 hours, adding 8 briquettes to each charcoal pile every hour.
Baste the ribs: Transfer 1 cup sauce to a small serving bowl. Brush both sides of ribs with remaining 1 cup sauce. Cover, and grill until ribs are glistening and deep mahogany, about 15 minutes. Let stand for 10 minutes. Serve with reserved sauce.
If your charcoal grill doesn't have a built-in thermometer, monitor its temperature by inserting a candy or deep-frying dial thermometer into one of the kettle's top vents.