The Flank SteakThe flank steak is cut from the belly muscles of the cow. Long and flat, the flank steaks most notorious recipe is for London Broil. Though the dish did not originate in London. Recently, the popularity of the London Broil has driven up the prices of the flank steak. Though, it still remains one of the most affordable steaks on the market.
The flank steak is a tough steak and therefore most recipies use a marinade or reuqire that you braise the meat. Marinades can either be acidic with ingredients such as vinegar, lemon juice or wine (typically a sweet flavor) or, a savory flavor with typically a salt base (many times with a soy sauce). Be very cautious when using an acid based tenderizer, as it can make the flank steak mushy, especially when using unpasturized juices. This is because many of the enzymes are still active in the juice, where as the pasturization process kills them, and you only have an acid tenderizing the meat.
The other technique comes about from the interaction that occurs when salt is applied to the meat. When you find a recipe with a soy sauce base for the marinade, the active ingredient is the salt. I have found that when marinating with a salt based marinade is better for a flank steak. However, as the Flank is so thin, a long marinade time can give the meat a very salty taste.
Using a spice rub, will give your flank steak a very nice dark brown, flavorful crust. A spice rub, however, did not help to tenderize the meat. Another concern, with a rub, is that the spice will burn if it is cooked too long (medium or more). So if you want to have a well done, piece of meat, then passing a sauce around the table will help to add flavor, if you are not using a marinade to add flavor.
Every source, I have seen on the flank steak has stated that it should be cooked for a short period of time over high heat. To check to see if the Flank Steak is done, a meat thermometer will not work, as the Flank is too thin. So one must resort to the primitive method of checking for doneness: Cut into the meat to see if it is done. Another method, as I learned in the restaurant industry, is to make a fist and touch your fore arm. The feel of your forearm, to the experienced, is similar to the feel of how a steak is cooked. With rare being nearer to your fist, moving towards well done when you hit the knot in the muscle in your forearm. You should always remember that the carry over heat will continue to cook the steak after it comes off the cooking surface. So to obatin a medium rare steak you need to take it off the heat when it appears rare, and so on.
After the meat has been cooked, you should let it "rest". While cooking, the juices are pushed to the center of the meat. This is especially true, when cooking over high heat. If you cut your meat immediately after it comes off the heat, much more of the juices will come out of the meat.
Allowing the meat to rest for several minutes allows for the juices to move back outward from the center, retain a larger percentage of the moisture. Cutting your steak too early after cooking can leave it looking gray and less tender, than if you were to wait a couple of minutes after cooking it, before you slice it.
I have found that cutting the flank on a bias, across the grain helps to make the steak more palatable.