1. Allow the flank steak to come to room temperature, then pat dry surface moisture with paper towels.
2. Coat both sides of the steak liberally with unrefined sea salt and coarse ground black pepper. Be generous. You are creating a crust.
3. While the meat comes to room temperature, heat a charcoal or gas grill to high heat.
4. You should be able to hold your hand about an inch over the grill grate for only 1 second before it feels too hot.
5. If using the stove, add tallow and/or coconut oil to a cast iron skillet and get the skillet searing hot.
6. Just as the oil seems it will begin to smoke, lay the steak in the pan and allow to sear on each side for 3-7 minutes depending on the level of doneness you desire.
7. Otherwise, set the steaks on the grill and allow to sear on each side undisturbed for 3-7 minutes depending on the level of doneness you desire.
8. Use a meat thermometer to measure the center temperature: (Rare = 120F Medium Rare = 125F Medium = 130F).
9. NOTE: Do not take a flank steak past medium as it will continue to cook when taken off the heat source.
10. Place the flank steak on a wooden board or serving platter and leave undisturbed for 10 minutes. This will allow the juices to run back through the meat instead of escaping.
11. Slice in thin strips across the grain.