Remove steaks from refrigerator 45 minutes before cooking. Pat completely dry with paper towels - this is crucial for a good crust. Season aggressively on all sides with kosher salt and black pepper. The salt needs time to penetrate, so don't rush this.

In a small bowl, combine the cold butter cubes, minced garlic, and leaves from 2 thyme sprigs (strip them off with your fingers). Mash together with a fork until well blended. Set aside.

Heat your cast iron skillet over high heat until it just starts to smoke, about 4 minutes. Add the oil and swirl to coat. Lay steaks in the pan and don't move them. Sear for 4 minutes until a deep brown crust forms. Flip and sear the other side for 3 to 4 minutes more. For the last minute, stand steaks on their fat cap to render it down.

Reduce heat to medium-low. Add the garlic butter mixture, remaining thyme sprigs, and rosemary to the pan. Once the butter melts and foams, tilt the pan and spoon the butter over the steaks continuously for 1 to 2 minutes. The butter should turn nutty brown and smell amazing, not burned. Check temperature - pull at 125F for medium-rare.

Transfer steaks to a cutting board and pour the pan butter with all the garlic and herbs over top. Let rest for 5 to 7 minutes. This redistributes the juices. Slice against the grain, sprinkle with flaky salt, and serve with the pan drippings spooned over.