2 pounds boneless chicken thighs—skinned, trimmed and cut into 1-inch
1 small green bell pepper, cut into 3/4-inch squares
1 leek, white part only, halved lengthwise and cut crosswise into 3/4-inch
In a small saucepan, combine the sake, mirin, miso, soy sauce, sugar and ginger. Simmer the sauce over moderately low heat until it is thick and shiny, about 15 minutes.
Meanwhile, thread the chicken, bell pepper and leek onto twelve 8-inch wooden skewers, alternating the ingredients and beginning and ending with chicken. Set the skewers on a foil-lined rimmed baking sheet.
Preheat the broiler and set a rack 4 inches from the heat. Cover the exposed ends of the skewers with foil and brush the skewers on both sides with the sauce. Broil the skewers for 4 to 5 minutes on each side, basting when you turn them, until the chicken is cooked through and browned at the edges. Serve the chicken yakitori hot or at room temperature.
The recipe can be prepared through Step 2 up to 1 day ahead; refrigerate the skewers and sauce separately.