Negimaki—grilled beef rolled around scallions and grilled with a sweet and savory teriyaki-style glaze—is one of my favorite Japanese appetizers. Here we've Super Mario mushroom'd it to full main course-sized proportions, stuffing a butterflied flank steak with an aromatic scallion-ginger oil before grilling it over hot coals and serving it with a teriyaki sauce.
I first tried this recipe cooking it exactly as I would a negimaki—stuffing the flank steak with raw scallions. It didn't work out so well; The scallions stayed raw, developing an off-putting steamed texture. Instead, I opted to adopt a technique used for making Hainnanese Ginger-Scallion Oil—pouring heated oil over thinly sliced scallions and ginger and letting them steep until cooled.
That worked like a charm. The hot oil cooked the scallions just enough to help tame that steamed flavor. Ginger is not a traditional ingredient in negimaki, but it tasted so darn good I left it in.
Finally, I brushed the sauce over the steaks after searing them over the hot side of the grill. As the steaks slowly finish cooking over the cool side, the homemade Teriyaki Sauce reduces into a rich, shiny lacquer that coats the beef in a sweet-and-savory glaze.