In a small bowl, combine the ancho powder, black pepper and cinnamon. Sprinkle the seasoning mix all over the lamb chops and let stand at room temperature for 30 minutes.
Meanwhile, bring a medium saucepan of salted water to a boil. Add the pearl onions and cook until barely tender, about 4 minutes; drain. When the onions are cool enough to handle, cut off both ends and carefully peel, keeping the onions intact.
Preheat the oven to 375°. Season the lamb chops with salt. In a large ovenproof skillet, heat the oil. Add the lamb chops fat side down (the edge of the chops) and cook over moderate heat until lightly browned, about 2 minutes. Turn the chops to one (flat) side and cook until lightly browned, about 2 minutes. Turn the chops over and add the onions to the skillet. Transfer the skillet to the upper third of the oven and roast the chops for 8 minutes. Turn the chops and roast for 2 minutes longer, until medium-rare. With a slotted spoon, transfer the chops and onions to a warm platter.
Tilt the skillet and carefully spoon off most of the fat, leaving the lamb juices behind. Add the red wine to the skillet and bring to a boil, stirring to scrape up the browned bits, about 1 minute. Stir in the beef broth, coffee and tomato paste and boil, stirring, until reduced to 3/4 cup, about 3 minutes. Tilt the platter with the lamb and pour any accumulated juices into the skillet. Remove the skillet from the heat and swirl the butter into the sauce. Season with salt and pour the sauce over the chops. Serve the lamb chops right away.