Score Fatty side of flank steak. Pour the soy sauce and a resealable plastic bag . Rub Sugar on both sides of meat and place in plastic bag to marinate for two hours+/-.

Preheat a large cast-iron skillet on high to 425°F. rinse and pat dry steak.

Add 2 tablespoons butter to skillet , add steak, cook about 6 to 7 minutes for rare per side , depending on the thickness and how well done you want your steak.

Serve with salt and pepper , really no condiments needed