From America's Test Kitchen Season 9: Backyard Steak and Potatoes
A common way to prepare flank steak is to marinate it in a bottle of Italian-style salad dressing. But while the resulting flavor can be interesting, the acid in the vinegar can ruin the texture, making the exterior mushy and gray. We wanted to develop a fresh, Mediterranean-style marinade without acid—a marinade that would really boost flavor without over-tenderizing the meat.
We turned to the optimal method for cooking a flank steak—use a two-level fire (which lets you move the thin part of the steak to the cooler side of the grill once it is done), cook the steak only to medium-rare to keep it from getting tough, and let the steak rest before slicing to reduce the loss of juices. Now we could concentrate on developing and applying an acid-free marinade.
Because fat carries flavor so well, we knew oil would be a key ingredient—the challenge was to infuse Mediterranean flavors (garlic, shallots, and rosemary) into the oil and then into the steak. We developed two key steps. First, we minced the aromatics and combined them with the oil in a blender to create a marinade paste. Next, we invented a novel "marinating" technique— prick the steak all over with a fork, rub it first with salt and then with the marinade paste, then let it sit for up to 24 hours. After marinating, the paste is wiped off to prevent burning, and the steak is ready for the grill. Our technique was so successful, we were free to create two more marinades—one with Asian flavors, and the other with a smoky-spicy kick.
Flank steaks smaller or larger than 2 pounds can be used, but adjust the amount of salt and pepper accordingly. We prefer flank steak cooked rare or medium-rare. If the steak is to retain its juices, it must be allowed to rest before being sliced. If using a gas grill, cook the steak over high heat, following the times in step 3, but keep the cover down. If the meat is significantly underdone when tested with a paring knife, turn off one burner and position the steak so that the thinner side is over the cool part of the grill and the thicker side is over the hot part of the grill.