In a bowl, combine garlic, parsley, mustard, olive oil, red wine, black pepper, and rosemary; mix together well.
In a shallow baking dish, season the steaks moderately with salt and pepper. Cover the steaks with the marinade mixture and cover the dish with plastic wrap. Allow to marinate in the refrigerator for at least 1 hour or overnight. Remove steak from refrigerator and bring to room temperature before cooking.
Rare - 120 degrees F
Medium Rare - 125 degrees F
Medium - 130 degrees F
What constitutes rare and medium-rare cooked meat? To satisfy government home economists, the Beef Council says rare beef means an internal temperature of 140 degrees F. Well, that is ok if you like well-done and dry meat. If you like moist, rosy meat (like I do), rare begins at 120 degrees and starts to become medium rare at 125 or 130 degrees F. To cook your meat properly, you must purchase and use a good instant-read digital meat thermometer.
Slice the meat into thin slices across the grain.
Makes 4 to 6 servings.
Flat Iron Steak with Red Wine and Rosemary Recipe: https://whatscookingamerica.net/EricTurner/FlatIronSteak.htm