Dry-brine (optional but best): Pat the steak dry. Season all sides evenly with kosher salt. Place on a wire rack set over a baking sheet and refrigerate uncovered 1–24 hours. If short on time, salt at least 45 minutes before cooking.
Low & slow: Preheat oven to 225°F (107°C). Pepper the steak. Set it on the wire rack/baking sheet and insert a probe thermometer if you have one. Roast until the internal temperature reaches 115°F (46°C) for medium-rare (about 30–60 minutes, depending on thickness) or 10°F (6°C) below your final target (see Doneness Guide).
Preheat for sear: Heat a cast-iron skillet over high heat until just smoking, 2–3 minutes. Add the oil.
Hard sear: Sear the steak 45–60 seconds per side until deep brown. Use tongs to hold and render the fat cap/edges for 20–30 seconds.
Butter baste: Reduce heat to medium-high. Add butter, garlic, and herbs. Tilt the pan and spoon foaming butter over the steak for 30–60 seconds per side until the internal temp hits 125–130°F (52–54°C) for medium-rare.
Rest & serve: Transfer to a board, rest 5–10 minutes. Slice against the grain, finish with flaky salt, and spoon over pan butter.
