This recipe is a crowd pleaser that should be made at least a day in advance so it can marinate. Make enough to have leftovers...they are perfect for making sandwiches with.
If you don't have a container to marinate, use a large Ziplock bag to place the meat in to marinate. I find the longer it marinates, the better. Be sure to flip the meat a few times a day to make sure every inch of it gets marinated. I also think it tastes better when you really score the meat on both sides with a knife. This allows the marinade to get deep into the meat.
Score flank steak with 1/8"cuts ( deep and apart) on both sides of flank steak.
In a small bowl, whisk together brown sugar, soy sauce, sherry, sesame oil, sesame seeds, garlic, ginger, scallions and pepper.
Marinade 24 hours or overnight.
Grill for 3 minutes on each side for rare. Add more time to get meat to desired doneness.
The steak tastes best when sliced very thinly. Place on serving dish and garnish with chopped grilled scallions.