Flank steak is best marinated for at least 4 hours and up to 24 hours.
Marinate flank steak for as long as you can. About 2-12 hours is ideal. Whatever you have time for!
Heat a cast iron skillet to high heat. Sear steak for 2-3 minutes a side depending on thickness.
Let steak rest for at least 5 minutes
Cut the meat in very thin slices, at an angle, across the grain of the meat. This way you break through the tougher muscle fibers and your meat will have a better texture!