Pat flank steak dry with paper towels
Season all over with salt and black pepper
Optional marinade: soy sauce, olive oil, garlic, ginger, brown sugar or honey, and lime juice; marinate 2–12 hours in the refrigerator
Preheat oven or grill to high heat
For best results, cook to medium-rare: 130–135°F (54–57°C) internal temperature
Grill method: preheat grill, oil grates, cook 3–5 minutes per side for medium-rare (time varies by thickness)
Stovetop method: heat a heavy skillet until very hot, add a thin layer of oil, sear 3–5 minutes per side for medium-rare
Oven method (reverse sear): roast at 425°F (220°C) until 110–120°F (43–49°C), then sear 1–2 minutes per side
Rest steak 8–15 minutes before slicing
Slice against the grain into thin strips (about 1/4–1/2 inch thick)
Optional finishing: brush with reserved marinade (boiled 2–3 minutes first), sprinkle with fresh herbs, or add a quick sauce (chimichurri, salsa verde, or garlic butter)