Using a sharp knife, score the steak on both sides with shallow cuts (¼") across the grain in two directions. You will have a criss cross effect. (See photo in post)
Season the steak on both sides with pepper.
Whisk together all of the marinade ingredients.
In a glass bowl or a re-sealable freezer bag, submerge the steak in the marinade.
Refrigerate and allow the steak to marinate at least four hours or up to 8 hours.
Remove the steak from the marinade and set the marinade aside if using it to make the optional red wine sauce. If not, discard the marinade. Pat the steak dry with paper towels and allow it to come to room temperature, about 30 minutes.
Lightly oil the cooking surface in your air fryer.
Preheat the air fryer to 400°
Cook the steak 5 minutes on each side, flipping only once.
Remove the steak and allow it to rest on a cutting board 5-7 minutes.
Slice the steak diagonally, across the grain into thin slices.
Serve with Red Wine Sauce (optional, see below)
Red Wine Sauce
Pour marinade and beef broth into a skillet. Bring to a boil, then reduce heat and simmer until sauce reduces and thickens. Stir in butter one piece at a time. Taste and add salt and pepper if necessary.
This recipe is gluten-free if you use gluten-free soy sauce or tamari.Remove the steak from the marinade and allow it to come to room temperature 15-30 minutes before cooking. Keep the marinade to make the optional sauce, or discard it.Even if your air fryer manufacturer says there's no need to preheat it, you should preheat for the steak to cook perfectly.Score the meat before marinating it. This step severs the long fibers to help tenderize the meat, and it allows the marinade to penetrate for maximum flavour.Make sure to cover the steak completely in the marinade. If not, turn it frequently.Only turn the flank steak once, halfway through cooking, and do it quickly so as not to release too much heat.Cook flank steak to medium rare or medium. Well done flank steak, unless it's slow cooked, will be tough.Using a meat thermometer, internal temperatures should be: rare 125°, medium rare 135°, and medium 145°.Allow the steak to rest before slicing to allow the juices to redistribute.Thinly slice flank steak across the grain diagonally, for maximum tenderness.For grilled flank steak, follow all of the instructions before and after the air fryer. Substitute "grill" for air fryer and that's it!