In a large cast-iron skillet, heat the oil over medium-high heat until it just begins to smoke. Add the steak and cook, turning occasionally, until nicely seared on both sides and the internal temperature is 110˚F for rare, 120°F for medium-rare, or 130˚F for medium, 6 to 12 minutes, depending on desired doneness. A couple of minutes before the steak is done, add the garlic cloves and thyme sprigs to the pan and turn them occasionally.