Flank steak is the perfect cut for for feeding a crowd quickly and deliciously. It's relatively affordable for its size (especially compared with pricier cuts like sirloin or rib-eye), and when cooked properly, it's tender and juicy. A quick marinade pairs perfectly with this lean cut, and truly improves the flavor without adding too much fuss.
Prepare the marinade. Combine the garlic, rosemary, olive oil, balsamic vinegar, and salt in a large mixing bowl. Whisk until the oil and vinegar emulsify.
Place the steak into the marinade. Using your clean hands, work the marinade into the steak until well coated. Set aside to marinade at room temperature for at least 15 minutes, but not longer than 1 hour.
While the steak is marinating, prepare your grill for high heat.
Grill the steak 4 minutes per side for medium-rare to medium, or until an instant read thermometer reads 130°F. See the temperature guide in the body of the post. For best texture, do not cook above 140°F.
Remove the steaks from the grill and transfer to a cutting board. Season with additional salt and cracked black pepper to taste. Rest 10 minutes. Slice thinly against the grain, then sprinkle with additional chopped rosemary. Serve immediately. Leftovers keep in the fridge for approximately 3 days in a tightly sealed container and are delicious cold.
If your steak is more square than rectangular, slice lengthwise into 2 long rectangles. This will help you cut more even slices after grilling. This steak is delicious on its own, but if you prefer your steak with a sauce, it's perfect with pesto.