01 - In a large mixing bowl, whisk together the soy sauce, mirin, honey, brown sugar, rice vinegar, minced garlic, grated ginger, and sesame oil until fully combined.
02 - Add the chicken thighs to the bowl and turn each piece to coat thoroughly. Cover and refrigerate for at least 30 minutes, or up to overnight for deeper flavor penetration.
03 - Preheat the oven to 400°F (200°C). Line a baking tray with parchment paper or aluminum foil for easier cleanup.
04 - Remove the chicken thighs from the marinade, reserving all the liquid. Place the thighs skin-side up on the prepared baking tray, spacing them evenly apart.
05 - Roast the chicken for 35 to 40 minutes. After the first 20 minutes, baste generously with the reserved marinade. Continue roasting until the internal temperature reaches 165°F (75°C) and the skin turns golden and caramelized.
06 - While the chicken roasts, pour the remaining marinade into a small saucepan and bring to a rolling boil. For a thicker glaze, dissolve the cornstarch in water and stir it in. Simmer for 3 to 5 minutes until the sauce is glossy and coats the back of a spoon.
07 - Transfer the roasted chicken thighs to a serving platter. Drizzle with the reduced teriyaki sauce and garnish with sliced green onions and toasted sesame seeds. Serve immediately while hot.