Broiled Beef–Scallion Rolls

Wrap meat in plastic wrap and chill in the freezer until very cold but not frozen solid, about 2 hours. Meanwhile, put mirin, soy sauce, and sake into a small pot and bring to a boil over high heat. Pour half the sauce into a small bowl and set aside. Dissolve potato starch in 5 tsp. cold water in another bowl. Return pot with remaining sauce to high heat and bring just to a boil. Add potato starch mixture, stirring constantly until sauce thickens, about 20 seconds. Set aside.

Preheat broiler. Using a very sharp slicing knife, slice meat across the grain into four 1⁄4"-thick slices, then halve each crosswise. Put 1 piece of meat on a sheet of plastic wrap and cover with another sheet. Using a meat pounder, pound meat into a 1⁄16"-thick rectangle about 3 3⁄4" x 6"; set aside. Repeat with remaining meat.

Heat a medium broiling pan under broiler until hot. Meanwhile, put 1 piece of meat on a clean surface with one of the narrow ends facing you. Put 6–7 of the scallion pieces along edge of meat closest to you and roll up snugly. Repeat with remaining meat and scallions.

Put rolls into hot pan, pour unthickened sauce on top and broil for 5 minutes. Transfer rolls to a cutting board, slice in half on the bias and return to pan. Spoon half the thickened sauce over rolls and broil for 2 minutes more. Spoon remaining thickened sauce over rolls. Serve with steamed vegetables, if you like.