Heat the olive oil in a large ovenproof sauté pan over high heat. Season the lamb on all sides with salt and pepper. Sear all sides of the lamb rack until browned, about 5 minutes total. While searing, baste often with the oil from the pan, especially in the areas around the bones. Once seared, reduce the heat to medium and add the butter, garlic, and thyme. Allow the butter to foam, and continue basting for 2 minutes. Transfer to the oven for 5 minutes, flip, and return to the oven for 3 more minutes, or until the internal temperature reaches 125°F. Rest the lamb in a warm area, covered with foil, for 10 minutes, or until the internal temperature reaches 138°F. Remove the twine and keep warm.