Season steak on both sides with the salt and place on a rack set inside a rimmed sheet pan. Refrigerate for at least 6 hours, or up to 24.
Heat oven to 200ºF. Insert a probe thermometer horizontally through the side of the steak and roast, still on the rack and sheet pan, until it reaches an internal temperature of 120ºF, about 1 hour. Remove steak from the oven and rest, uncovered, for 10 minutes.
Meanwhile, place a 12-inch cast iron skillet over high heat until it reaches at least 600ºF, at least 10 minutes. (If you don't have an infrared thermometer, you'll know you're close when 1/2 teaspoon water dropped in the middle of the pan has completely evaporated in 5 seconds.
Brush a very light coat of peanut oil onto both sides of the steak. Transfer to the hot skillet and sear on each side until deeply browned, 45 seconds per side. Use a stopwatch!
Transfer to a clean rack and let rest for 5 minutes. Slice diagonally against the grain to serve.