Generously season steak with Kosher salt and pepper; let sit at room temperature 1 hour.
Heat a dry skillet, preferably cast iron, over medium high and add oil. As soon as oil is smoking, add the steak. Turn every 2 minutes or so until a deep brown crust forms and the internal temperature is a few degrees below your favored doneness (aim for 120°–125° for medium rare), about 6-8 minutes.
Add butter, thyme or rosemary, and garlic to skillet. Tilt pan toward you so butter pools on one side, and use a large spoon to continually baste steak with butter. Continue until butter is no longer bubbling, it smells nutty, and is beginning to brown, about 1 minute. Transfer meat to a cutting board and let rest 10 minutes before slicing. Finish with the flaky salt.