Take the steaks out of the refrigerator about 45–60 minutes before cooking. Pat dry with paper towels, then season both sides with steak seasoning. Let rest at room temperature, uncovered, so the surface dries slightly—this helps create better sear.
Heat a large cast‑iron or heavy stainless‑steel skillet over medium‑high to high heat until it just begins to smoke. Swirl in the oil.
Place the steaks in the skillet in a single layer—avoid crowding—and cook for 1-2 minutes per side, depending on thickness, until browned and sizzling. Transfer to a warm platter and tent with foil.
Reduce heat to medium. Add the butter to the skillet. When melted and foaming, stir in the crushed garlic and rosemary sprigs. Sauté for 30–60 seconds, just until fragrant.
Spoon the garlic butter over the steaks and garnish with sautéed rosemary (or discard). Slice against the grain, if desired, and serve immediately.