Cast iron is the closest a home cook gets to a steakhouse broiler. It holds heat brutally well, which is exactly what a great crust needs. Here is the method that works on any stove.
Buy the right cut and dry it
A thick steak, at least an inch and a half, gives you room to build crust without overcooking the inside. Ribeye and strip are forgiving. Pat the surface completely dry with paper towels and salt it generously at least 40 minutes ahead, or right before cooking. Surface moisture is the enemy of a sear.
Get the pan screaming hot
Heat the dry skillet over high heat for five full minutes. It should be just starting to smoke. Add a thin film of a high-smoke-point oil, then lay the steak down away from you.
- Do not move it for two to three minutes
- Flip when a deep brown crust has formed
- Sear the second side for another two to three minutes
Baste and rest
In the last minute, drop in butter, a smashed garlic clove, and a sprig of thyme. Tilt the pan and spoon the foaming butter over the steak. This is the single move that separates good from restaurant-good.
Pull the steak at about 125 degrees for medium-rare; it will climb another five degrees as it rests. Rest it on a board for at least five minutes so the juices redistribute. Slice against the grain and finish with flaky salt.