Instructions

• If using wood chips, soak them in water for at least 30 minutes (no need to soak wood chunks).
  If using wood chips, soak them in water for at least 30 minutes (no need to soak wood chunks).
• Prepare the grill for indirect cooking over very low heat (225° to 275°F).
• In a small bowl stir together all the rub ingredients.
• Place the racks, bone side up, on a cutting board. If the racks still have the membrane attached, remove it: Using a dull knife, slide the tip under the membrane covering the back of each rack. Lift and loosen the membrane until you can pry it up, then grab a corner of it with a paper towel and pull it off.
• Season the racks on both sides with the rub, rubbing more of the mixture into the meaty side of each rack. In a medium bowl whisk together all the mop ingredients until the sugar dissolves.
• Add four wood chunks or drain and add four handfuls of wood chips to the grill, following manufacturer's instructions, and close the lid. When the wood begins to smoke, cook the onion halves and the sparerib racks, meaty side up, over indirect very low heat, with the lid closed, for 1½ hours.
  Cook the onion halves and the sparerib racks, meaty side up, above foil pan, over very low heat, with the lid closed, for 1½ hours.
• Using long tongs, transfer the onion halves to a cutting board. Check the racks at this point and, if the surface is starting to look dry, transfer them to a baking sheet to brush with the apple cider mop.
• After brushing both sides of each rack with the mop, add the remaining two wood chunks or drain and add the remaining wood chips to the grill. Cook the racks for 1½ to 3 hours longer. After each hour, brush each rack quickly with the mop, then rotate the position of each rack so they cook evenly. Keep the temperature of the grill between 225° to 275°F.
  After brushing both sides of each rack with the mop, continue cooking the racks for 1½ to 3 hours longer. After each hour, brush each rack quickly with the mop, then rotate the position of each rack so they cook evenly.
• While the ribs are cooking, peel and mince the smoked onion. Heat the oil in a medium saucepan over medium heat on the stove. Add the onion and cook, stirring occasionally, until very soft and golden brown, 5 to 10 minutes. Add the garlic and cook for 30 seconds, stirring frequently.
• Stir in the ketchup, vinegar, sugar, Worcestershire sauce, chili powder, and paprika. Reduce the heat to low and simmer, stirring frequently, until the sauce is thickened and reduced to about 2 cups, about 5 minutes.
• The ribs are done when the meat has shrunk back from the bones by at least ½ inch and you can easily slide a skewer through the meat between the bones. Another good test is to lift a rack by picking up one end with tongs. If the rack bends in the middle and the meat tears easily, the ribs are ready. Discard any remaining mop.
• When the ribs are ready, brush both sides of each rack generously with the onion sauce. Close the lid and continue to cook over indirect very low heat for 10 to 20 minutes.
  When the ribs are ready, brush both sides of each rack generously with the onion sauce. Close the lid and continue to cook, above foil pan, over very low heat for 10 to 20 minutes.
• Transfer the racks to a cutting board. Let rest for 5 to 10 minutes. Cut between the bones into individual ribs. Serve warm with the remaining sauce on the side.