1.
Combine vinegar, maple syrup, and mustard in a bowl. Measure 2/3 cup of mixture into a large plastic resealable bag, add the steak, and seal. Refrigerate for 1 hour. Reserve remaining marinade in refrigerator.
2.
Remove steak from marinade and discard bag with used sauce. Season both sides of meat with salt and pepper to taste.
3.
Heat your gas or charcoal grill to high (Here's how to tell if it's high: Hold your hand about four inches above the cooking surface. After 2 to 3 seconds, the heat will force you to pull your hand away.)
4.
Oil the grill grate, using an oiled rag.
5.
Place the steak on the grill. Use these cooking times to cook your steak to medium: 2 to 3 minutes per side for a 1/2 inch thick steak, 4 to 6 minutes per side for a 1 inch thick steak, 6 to 9 minutes per side for a 1 1/2 to 2 inch thick steak.
6.
While steaks are grilling, pour reserved marinade into a saucepan and place on medium-high heat. Bring to a boil, then let it cook for 2 minutes to reduce.
7.
Take the steak off the grill. Let it rest 2 to 3 minutes to allow the juices to reabsorb into the steak. Pour reduced marinade sauce over steak and serve.