For the ribs: Preheat the oven to 350 degrees F. Line a large rimmed baking pan with foil.
Place the ribs on the prepared baking pan meat-side up. Sprinkle them with the paprika, garlic powder, 1 tablespoon salt and a generous amount of pepper. Rub the spices all over the ribs.
Cover the pan tightly with foil and bake until the meat is very tender and can easily be pulled off the bone, about 2 hours.
For the barbecue sauce: Meanwhile, heat the oil in a medium saucepan over medium heat. Add the onions and 1/2 teaspoon salt and cook, stirring often, until very soft and golden brown, about 20 minutes. Add the garlic and cook, stirring, 1 minute. Add the ketchup, orange juice, Worcestershire, chipotles and adobo and 1/2 cup water. Increase the heat to bring to a boil, then reduce the heat to keep at a simmer until slightly thickened, about 10 minutes. Transfer to a blender and puree until smooth (be careful when blending hot liquids). Alternately, an immersion blender can be used in the pot.
Finish the ribs: Preheat the grill to medium-high (or set the oven to broil).
Reserve about a cup of the barbecue sauce for serving alongside the ribs. Brush a small amount of the remaining sauce on the bone side of the ribs and a generous amount on the meaty side.
Grill the ribs, meaty-side up, until the underside is lightly charred, about 3 minutes. Turn the ribs over and grill until the meaty side is charred in spots, 3 to 5 minutes (if using the oven, simply broil for 3 to 5 minutes). Transfer to a cutting board and cut each rack in half. Serve immediately with the reserved sauce on the side.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.