In a medium bowl, whisk together balsamic vinegar, minced garlic, Worcestershire sauce, sugar, black pepper and salt

Place the flank steak in a large resealable plastic bag or shallow dish. Pour the marinade over the steak, ensuring it's evenly coated. Seal the bag or cover the dish with plastic wrap. Refrigerate for at least 4 hours, but for best results, let it marinate overnight or up to 12 hours. The longer it marinates, the deeper the flavor will be.

When you're ready to cook, preheat your grill to high heat (around 450-500°F) or use a cast iron pan if grilling is not an option. If using the pan, heat it over medium-high heat.

Remove the steak from the marinade, allowing any excess to drip off. Grill the steak for about 4-6 minutes per side, depending on thickness, until it reaches your desired doneness. For medium-rare, cook until the internal temperature reaches 130-135°F. For medium, aim for 135-145°F.

Tip: If using a cast iron pan, sear the steak on both sides for 4-5 minutes, then finish it in the oven at 400°F for a couple of minutes, if needed.

Once the steak is done, remove it from the grill or pan and let it rest for 5-10 minutes. This allows the juices to redistribute, ensuring a juicy and tender result.

Slice the steak thinly against the grain. This step is crucial for maximizing tenderness, as cutting against the grain shortens the muscle fibers, making the meat easier to chew.

Garnish with fresh herbs, like parsley or cilantro, and serve with your favorite sides like grilled veggies, a fresh salad, or roasted potatoes.