Preheat the oven to 400°. In a medium skillet, heat 1 tablespoon of the oil until shimmering. Season the lamb with salt and pepper. Add the lamb to the skillet, fat side down, and cook over moderately high heat until richly browned, about 3 minutes. Turn the lamb fat side up and cook for 2 minutes longer. Transfer the skillet to the oven and roast the rack for about 20 minutes, until an instant-read thermometer inserted in the center of the meat registers 125° for medium-rare. Transfer the lamb to a carving board and let rest for 10 minutes.
Discard the fat in the skillet. Add the remaining 2 teaspoons of oil and the shallots to the skillet and cook over moderate heat until softened, about 3 minutes. Add the wine and simmer until reduced by half, about 2 minutes. Add the stock and bring to a simmer. Remove the skillet from the heat. Stir in the whole grain and Dijon mustards and the thyme. Season the sauce with salt and pepper.
Carve the lamb into chops and arrange on warmed plates. Spoon the sauce over the lamb and serve.