1-1/2 lb. skirt steak, trimmed of excess surface fat
Kosher salt and freshly ground black pepper
Looking at a raw skirt steak, it’s easy to see the lines of fat within the striations of meat. Don’t try to remove it. The fat adds flavor and bastes the meat as it melts away during cooking.
Combine the sugar, vinegar, Worcestershire, garlic, and rosemary in a baking dish or zip-top bag large enough to hold the steak. Add the steak and turn to coat. Let sit at room temperature for at least 5 minutes and up to an hour.
Prepare a high (500°F to 600°F) charcoal or gas grill fire. Take the steak out of the marinade and season both sides generously with salt and pepper. Cut into smaller pieces to make grilling more manageable, if you like.
Grill, flipping once, until grill marks form on both sides and cooked to your liking, about 3 minutes per side for medium rare (135°F). Transfer to a cutting board and let rest for 5 minutes. Slice against the grain and serve.