Salt each side of the flank steak with coarse salt. Massage the salt into the meat. Transfer the meat to a bag or pan.

Next, prepare the marinade. Add the balsamic vinegar, Worcestershire sauce, brown sugar, garlic, and Dijon mustard to a bowl and whisk until combined. Pour the marinade over the steak. Flip the meat around a few times to be sure it is fully coated. Cover and refrigerate for at least 30 minutes, but we highly recommend 2+ hours.*

While the meat is marinating, add all of the ingredients for the caprese topping to a bowl and mix to combine. Refrigerate until ready to serve.

When the steak is ready to cook, remove it from the refrigerator and let it rest at room temperature for 10-15 minutes.

Heat 2 tablespoons of oil in a large cast-iron skillet over medium/high heat. When the oil is hot, add the steak to the pan. Sear the meat for 4-7 minutes on each side (timing depends on the thickness of the meat) or until the internal temperature reaches 135-140ºF.

Remove the meat from the pan and let it rest for at least 10 minutes. Slice the meat thinly and against the grain, and top with the caprese salad.