Heat the oil in a medium saucepan over medium heat. Add the onions, garlic, chili powder and 1/2 teaspoon salt and cook, stirring occasionally, until the onions are softened, about 10 minutes. Add the bourbon and cook until slightly reduced, 2 to 3 minutes. Then add the ketchup, coffee, 1/2 cup water, brown sugar, cider vinegar and Worcestershire. Increase the heat and bring to a boil; lower the heat and simmer until slightly thickened and the onions are tender, about 25 minutes. Transfer the mixture to a blender and puree until smooth (be careful when blending hot liquids). Transfer the sauce to a bowl and cool slightly.
Preheat the oven to 325 degrees F. Line a baking sheet with heavy-duty aluminum foil.
Sprinkle the ribs with salt and pepper, and coat the racks on both sides with about 2 cups total of the barbecue sauce (reserve the remaining sauce). Put the ribs, bone-side down, on the prepared baking sheet and wrap each rack with foil. Bake until the meat is tender and pulling away from the bone, about 2 hours.
Remove the foil and turn the ribs bone-side up. Preheat the broiler to high. Brush the bone side of the ribs with half of the remaining sauce, and broil until lightly charred in spots, about 5 minutes. Turn the ribs over, brush with the remaining sauce and broil again until charred stops on top, another 5 minutes. Cut the racks in half and serve.
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.