Evenly season the steak with kosher salt on both sides. Place the steak in the refrigerator for one hour. Then, take it out of the refrigerator along with the compound butter and set them on the counter one hour before grilling the steak.
Light your grill and set it up for high direct heat. You’ll want to get the coals as hot and as close to the cooking grate as possible. If you’re using a gas grill, turn all burners to hi or max setting, close the lid, and allow the grill to preheat for at least 30 minutes, getting the grill grates as hot as possible.
Place the steak on the grill, directly over hot coals or burners and flip every 20 seconds. With each flip, place the steak in a different spot on the grill grate.
After about six minutes of total cook time, use a reliable quick read meat thermometer and start checking the internal temperature of the steak. Remove steak from the grill when the internal temperature reaches 115° F for a medium rare steak.
Top the steak with the compound butter, and tent it with aluminum foil. Allow the steak to rest for five minutes. Carry-over cooking will continue and the final serving temperature of the meat will be in the neighborhood of 125°F or so, the perfect medium rare.
Slice steak, top with optional finishing salt and serve hot.