In a medium bowl, whisk together the olive oil, balsamic vinegar, Worcestershire sauce, and soy sauce until well combined. Add the Dijon mustard, minced garlic, brown sugar, and red pepper flakes, stirring until the sugar dissolves and all ingredients are fully incorporated. This flavorful base will develop complexity as it sits with the meat. I like to taste the marinade before adding the steaks—if it needs more depth, a tiny splash of extra Worcestershire works wonders.

Pat the steaks dry with paper towels, then season both sides evenly with kosher salt and freshly cracked black pepper. Place the seasoned steaks in a container or resealable bag, then pour the marinade mixture from Step 1 over them, making sure each steak is fully coated. Refrigerate for at least 4 hours, or up to overnight if time allows—this gives the flavors time to penetrate the meat and develop a deeper, more complex taste.

Remove the steaks from the refrigerator 15-20 minutes before cooking to bring them closer to room temperature for even cooking. Heat a grill or cast-iron skillet to medium-high heat until it's very hot and just beginning to smoke. Remove the steaks from the marinade, allowing excess liquid to drip off, then place them directly on the hot surface. Cook for 5-7 minutes per side for medium-rare, depending on thickness—I like to resist the urge to move them around; letting them sit undisturbed creates a beautiful crust and locks in the juices. Let the cooked steaks rest for 5 minutes before serving to allow the juices to redistribute throughout the meat.