Remove the steak from the fridge and let it stand on the counter until it reaches room temperature, about 30 minutes. Preheat the oven to 250ºF. Place a wire cooling rack over a baking sheet. Mist the rack with cooking spray.
Pat the steak dry thoroughly with paper towels. Season generously all over with salt; sprinkle lightly with pepper. Place on the rack and bake until an instant-read thermometer stuck into the thickest part reads 120ºF for medium rare, 20 to 25 minutes (start checking after 15 minutes). Remove from the oven. Place a rack a few inches from the heat source and preheat the broiler to high.
Place the steak under the broiler and broil until just seared, turning over once, 1 to 2 minutes per side. Watch it carefully to prevent overcooking.
Transfer the steak to a cutting board, tent with foil and let rest for 5 minutes. Slice the steak against the grain and serve, sprinkling with flaky sea salt, if desired.