Wrap the porterhouse steak in plastic wrap or butcher paper and place it in the freezer for 1 hour. While the steak is freezing, preheat the oven to 200°F and position a rack in the center.

Remove the steak from the freezer and unwrap it. Pat the steak dry with paper towels.

Season both sides of the steak generously with kosher salt and freshly ground black pepper.

Place a cast-iron skillet (or other heavy skillet) on the stovetop over high heat and heat until very hot — at least 10 minutes.

Add a thin layer of safflower oil to the hot skillet. When the oil is shimmering, carefully set the steak in the skillet and sear one side only until a deep golden-brown crust forms, pressing the steak with tongs (or using a heavy-bottomed pot or press) to ensure even contact.

Transfer the steak, seared side up, to a rimmed baking sheet and place it in the preheated oven. Cook until the internal temperature reaches your desired doneness: 125°F for rare, 145°F for medium, or 165°F for well done. (Expect roughly 30 minutes to 1 hour, depending on oven and steak.)

Remove the steak from the oven, tent loosely with aluminum foil, and let it rest for 10 minutes.

Thinly slice the steak against the grain and finish with a final sprinkle of kosher salt if desired.