In a large airtight plastic bag combine trimmed sirloin, whiskey, and balsamic vinegar. Massage into the fibers of the meat. Place in the refrigerator for 1-2 hour(s).
Remove sirloin from the refrigerator and allow to come to room temperature for 30 minutes. Meanwhile, heat the grill.
Remove sirloin from the marinade and season with fine sea salt and freshly ground pepper to taste.
Preheat the grill to high heat. Place steak on the hot grill. If you are using a gas grill, cover the grill. Grill for 4-6 minutes on each side for medium rare. If you do not have a grill, you can follow the same instructions using the broiler of your oven on the second to top rack. Make sure to keep the door cracked and properly ventilate to not set off your smoke detectors.
Remove from heat and allow the meat rest for 5 minutes. Slice against the grain and serve.
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