Tender Marinated Flank Steak with a Flavorful Sauce

In a large dish or Ziploc bag, mix together the soy sauce, vegetable oil, dark brown sugar, Worcestershire sauce, Dijon mustard, garlic, chives, black pepper, and balsamic vinegar.
Marinate the Steak:

Add the flank steak to the marinade, ensuring it is well coated. Cover and refrigerate overnight or for at least 6-8 hours.
Grill the Steak:

Preheat a gas grill to high heat.
Remove the steak from the marinade and place it on the grill. Sear for 2 minutes per side.
Reduce heat to medium and continue cooking for 7-10 more minutes, flipping once, until the steak reaches an internal temperature of 130°F for medium-rare (or longer for medium).
Remove the steak from the grill and let it rest on a cutting board, loosely tented with foil, for at least 10 minutes.
Prepare the Sauce:

While the steak rests, pour half of the remaining marinade into a saucepan over medium heat.
Simmer for about 10 minutes, reducing slightly into a flavorful sauce.
Serve:

Slice the steak thinly against the grain.
Drizzle with the prepared sauce or serve it on the side.
Serving and Storage Tips: