Preheat a smoker to between 225° and 250°F for indirect cooking, using well- seasoned white oak. The wood should be burning in the flame, not smoldering. Let the steaks sit for about 45 minutes to come to room temperature.
Season the steak with the kosher salt and pepper on both sides, rubbing it evenly into the meat. Place the steak over the cool side of the grill and smoke the steak for 2 1/2 to 3 hours, flipping it halfway through, until the temperature reaches 120°F on an instant-read thermometer. Remove the steak from the smoker and let it rest on a carving board until cooled to 105°F.
While the steak is cooling, prepare a charcoal grill for direct high-heat grilling.
Once cooled to temperature, place the steak on the grill grate with the flame nearly touching the meat. Flip the steak often, every 1 to 2 minutes, until deeply, beautifully golden brown all over and the internal temperature reaches 125°F on an instant-read thermometer for rare.
Transfer the steak to the carving board, place the butter pats on the steak, and tent with foil for about 5 minutes. Uncover, slice the steak against the grain into 1/4-inch-thick pieces, and sprinkle with flaky salt. Serve with chimichurri on the side.