In a small bowl, combine all the ingredients. Set aside.
On a work surface, using paper towels, peel away the white membrane on the back of the ribs. Place the ribs on a large plate and sprinkle with the dry rub, rubbing thoroughly into the meat on both sides. Cover and refrigerate for 1 hour, or overnight.
With the rack in the middle position, preheat the oven to
Wrap the racks of ribs, two racks at a time, in aluminum foil lined with parchment paper (see note). Seal tightly and place
on a baking sheet. Bake for 2 hours or until the meat is tender.
Meanwhile, in a saucepan over high heat, soften the onion, garlic and chili powder in the butter for 2 minutes. Add the remaining ingredients. Bring to a boil and simmer over low heat for 40 minutes, or until the sauce has reduced by half. Season with salt and pepper.
In a blender, purée the sauce until smooth. Pour into
Preheat the grill, setting the burners to medium. Oil the grate.
Unwrap and drain the ribs. Grill for about 8 minutes, basting regularly with half of the sauce and turning halfway through cooking, until caramelized. Serve with the remaining sauce.
Using parchment paper prevents the bones from puncturing the aluminum foil.