Combine soy sauce, water, balsamic vinegar, and olive oil in a blender. Add the quartered onion and freshly peeled garlic cloves, then blend until completely smooth. I always use fresh garlic cloves rather than pre-minced—the flavor punch is noticeably sharper and more vibrant. Season with black pepper and blend briefly to incorporate.

Place the 2 lb beef in a large resealable bag or shallow dish. Pour the marinade from Step 1 over the meat, ensuring it's fully covered and coated on all sides. Seal the bag or cover the dish, then refrigerate for at least 6 hours or preferably overnight. The longer marinating time allows the flavors to penetrate deeply into the meat, creating a more complex and tender result.

Remove the marinated beef from the refrigerator 1 hour before you plan to cook it. This allows the meat to come to room temperature, which ensures more even cooking throughout. Pat the meat dry with paper towels to remove excess marinade—this step is crucial for achieving a good sear and caramelization on the grill.

Heat your grill to 450-500°F until it's smoking hot. Place the dried beef directly on the grill grates and cook for 8-12 minutes total, flipping every minute to develop an even crust while keeping the interior rare to medium-rare. I find flipping frequently prevents the exterior from burning while the interior stays perfectly pink. Use an instant-read thermometer to check doneness, aiming for an internal temperature of 130°F for medium-rare.

Transfer the cooked steak to a cutting board and tent loosely with foil. Let it rest for 10 minutes—this allows the juices to redistribute throughout the meat, ensuring each slice stays tender and juicy rather than running onto the plate. After resting, slice the meat against the grain into 1/2-inch thick slices, which maximizes tenderness. Serve immediately.