Prepare the Marinade: In a large zip-top bag (or a non-reactive container), combine all the marinade ingredients: balsamic vinegar, soy sauce, olive oil, minced garlic, minced rosemary (or dried rosemary), brown sugar, kosher salt, black pepper, and cayenne pepper (if using). Seal the bag tightly, removing as much air as possible, and massage the marinade to ensure all ingredients are well combined.

Marinate the Steak: Place the steak(s) in the marinade bag. Ensure the steak is coated evenly with the marinade. Seal the bag again, removing any excess air. Massage the marinade into the steak for about 30 seconds. This helps the flavors penetrate the meat.

Refrigerate: Place the bag in the refrigerator and marinate for at least 6 hours, or preferably overnight, for maximum flavor infusion.

Prepare for Cooking: Remove the steak from the refrigerator about 30 minutes before cooking to allow it to come to room temperature. This helps ensure even cooking. Remove the steak from the marinade bag and discard the marinade (do not reuse). Pat the steak dry with paper towels. This is crucial for achieving a good sear.

Cook the Steak: Heat 1 tablespoon of olive oil in a heavy-bottomed skillet, preferably cast iron, over medium-high heat until it is shimmering. Place the steak in the hot skillet. Cook for 4-5 minutes per side for medium-rare, or adjust the cooking time based on the thickness of your steak and your desired level of doneness (see internal temperature guide below).

Rest: Remove the steak from the skillet and place it on a cutting board. Let it rest for 5-10 minutes before slicing. This allows the juices to redistribute, resulting in a more tender and flavorful steak.

Slice and Serve: Slice the steak against the grain into thin slices. Serve immediately and enjoy!