Instructions

1. Place 1 1/4 cups soy sauce, 3/4 cup mirin, 1/2 cup sake, and 2 tablespoons packed brown sugar in a small saucepan. Bring to a simmer over medium heat, stirring constantly, until the sugar is dissolved, about 2 minutes. Reduce the heat to medium-low and simmer, stirring frequently, until reduced by half, syrupy, and thick enough to coat the back of a spoon, about 8 minutes.
2. Trim 2 medium bunches scallions, then cut the whites and light green parts crosswise 1 1/2-inch pieces; reserve the dark greens parts for another use. Cut 8 ounces boneless, skinless chicken thighs lengthwise into 1/4-inch-wide strips.
3. Skewer the chicken and scallions onto 12 wooden skewers: For each one, thread a slice of chicken lengthwise onto the skewer, skewer a piece of scallions horizontally next to the chicken, and then thread a second slice of chicken lengthwise.
4. Heat a cast iron or nonstick grill pan or wide frying pan over medium-high heat. Add as many skewers as will fit with 1/2-inch space between skewers. Cook, flipping every 2 minutes, for 6 minutes total. Baste with the sauce and continue to cook, flipping and glazing every 2 minutes, until golden brown and slightly charred, about 10 minutes more. Repeat cooking the remaining skewers if needed.
5. Arrange a rack 6 to 8 inches from the broiling element and heat the broiler to high.
6. Line a rimmed baking sheet with aluminum foil, then coat the foil with cooking spray. Arrange the skewers in a single layer on the baking sheet with 1/2-inch space between. Broil, flipping every 2 minutes, for 6 minutes total. Baste with the sauce and continue to broil, flipping and glazing every 2 minutes, until golden brown and slightly charred, 8 to 10 minutes more.