Prepare the ribs: Place the ribs bone-side up on a work surface. Starting at one end, insert the tip of a knife between the membrane and the bones to loosen the membrane, then pull it off. Flip the ribs so they are meat-side up. Rub each rack with 1 tablespoon scotch, if using. Combine the brown sugar, 5 teaspoons salt, 1 teaspoon pepper, the ground ginger and paprika in a small bowl. Rub the ribs on both sides with the spice mixture. Wrap each rack in heavy-duty foil, then wrap in another layer of foil, making sure the seam is on the opposite side to prevent leaking. Refrigerate 8 hours or overnight.
Preheat a grill to medium low (350 degrees F on gas or 335 degrees F on charcoal). Put the foil-wrapped ribs meat-side down on the grates. Grill, carefully flipping the ribs every 30 minutes, until the meat is tender but not falling apart and the tip of a paring knife inserted into the ribs meets slight resistance, 1 to 1 1/2 hours. (If using charcoal, add more coals as needed so the temperature stays between 300 degrees F and 325 degrees F.)
Meanwhile, make the barbecue sauce: Heat the vegetable oil in a medium saucepan over medium heat. Add the onion, garlic and fresh ginger and cook, stirring often, until just beginning to brown, 5 to 6 minutes. If using the scotch, remove the pan from the heat and stir in the scotch, then return to the heat and cook until almost dry, 1 to 2 minutes. Stir in 1/2 cup water, the ketchup, brown sugar, vinegar, soy sauce, mustard, chili-garlic sauce and 1/2 teaspoon pepper. Bring to a simmer and cook, stirring occasionally, until thick and glossy, about 30 minutes; you should have about 1 1/2 cups sauce. Transfer to a blender and puree until smooth. (You can make the sauce up to 1 day ahead; refrigerate until ready to use.) Divide the sauce between 2 bowls—half for cooking and half for serving.
When the ribs are ready, transfer to a baking sheet. Unwrap and discard the foil and any accumulated juices. Brush the meat side with the barbecue sauce and return to the grill, meat-side up. Cover and grill, moving the ribs around to prevent flare-ups, until the sauce cooks in, about 5 minutes. Brush the ribs with more sauce, flip and cook until lightly charred, 2 to 3 minutes. Flip the ribs so they’re meat-side up again, brush with more sauce and grill 5 more minutes. Flip the ribs again and brush the bone side with sauce, then flip again and brush the meat side one last time. Transfer to a cutting board and let rest 15 minutes.
Cut the racks into individual ribs. Serve with the reserved barbecue sauce.