How to Make It
Preheat the oven to 425°. Season the lamb racks all over with coarse salt and pepper. Heat 1 tablespoon of the oil in a large skillet and the remaining 1/2 tablespoon of oil in a medium skillet; both skillets should be ovenproof. Add 2 of the lamb racks to the large skillet and 1 rack to the medium skillet, meaty side down. Cook the racks over moderately high heat until well browned, about 4 minutes. Turn the racks and brown the other side, about 3 minutes longer.
Transfer the skillets to the oven and roast the lamb for 15 to 20 minutes, or until an instant-read thermometer inserted in the thickest part of the meat registers 120°or rare and 125° for medium rare. Transfer the racks to a carving board and let rest for 10 minutes.
Meanwhile, set the medium skillet over high heat. Add 1/2 cup of the wine and bring to a boil, scraping up any browned bits. Pour the wine into the large skillet and add the garlic and thyme. Set the large skillet over high heat, add the remaining 1/2 cup of wine and boil until reduced by one-third, about 3 minutes. Add the chicken stock and boil until reduced to 1/2 cup, about 8 minutes. Remove the skillet from the heat and discard the garlic and thyme sprig. Whisk in the butter, 1 piece at a time. Season with salt and pepper and strain the sauce into a warmed gravy boat.
To serve, cut the lamb into chops and arrange 3 chops on each dinner plate. Pass the Cabernet sauce at the table along with a little coarse salt for sprinkling on the lamb.
Have your butcher french the lamb by scraping the fat and gristle from the bones.