I've already outed my shameful seafood aversion. Yes, I am "that guy" who relies on teriyaki and tempura at standard Japanese restaurants. I switch it up sometimes though, getting negimaki—scallions wrapped with thinly sliced flank steak in a teriyaki sauce—thinking of it as "meat sushi" so I fit in better with all my raw seafood eating comrades.
Making negimaki at home, I quickly learned that my skills with working with smaller meat beef rolls were severely lacking. But whatever was lost in presentation, was more than made up for in flavor, as I felt these little rolls trumped what I'm used to at my local Japanese joint.
Why? Blanching the scallions creates less chew and makes them work better with the steak. Second was a marinade that infused the beef with teriyaki flavor, which was later reduced to a sauce and drizzled on top. Third was the grill, whose high heat formed an excellent sear on the tiny rolls. This delicious combo just further solidified my seafood aversion—who needs fish when "meat sushi" is so good?
Bring 2 quarts of water to a boil in a medium pot over medium-high heat. Add 1/2 tablespoon of salt, then blanch scallions until just softened, about 45 seconds. Remove scallions to a bowl of ice water. Transfer scallions to paper towels to drain and pat dry.
Cut flank steak with the grain, holding a large knife at a 30-degree angle to cutting board, into 12 1/8-inch-thick slices that are 1 1/2 to 2 inches wide. Arrange slices 1 inch apart on plastic wrap, then cover with another piece of plastic wrap and pound slices until about 1/16 inch thick.
Arrange 3 beef slices side by side, overlapping slices slightly to form a 6-inch square. Sprinkle square lightly with salt, then lay 3 scallions across the meat in the direction of the grain. Tightly roll up meat around scallions and tie shut with kitchen twine at ends and where meat slices overlap. Repeat with remaining meat and scallions.
Stir together sake, mirin, soy sauce, and sugar in a small bowl until sugar is dissolved. Put rolls in a small dish and pour marinade over them, turning to coat. Marinate, turning occasionally, while preparing the grill, 15 to 30 minutes.
Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over entire surface of coal grate. Set cooking grate in place, cover grill and allow to preheat for 5 minutes. Clean and oil the grilling grate. Grill rolls, reserving marinade, until well seared on all sides, 2 to 3 minutes per side. Transfer to a cutting board and let rest for 5 minutes.
While the meat is resting, pour reserved marinade into a small pot. Bring to a boil over medium heat and cook until slightly thickened, 3 to 5 minutes. Cut off and discard twine from negimaki rolls. Cut eat roll into 6 1-inch slices. Arrange rolls on a plate and drizzle with sauce.