01 - In a large bowl, whisk together miso paste, soy sauce, mirin, honey, sesame oil, garlic, ginger, rice vinegar, and black pepper until completely smooth and well combined.
02 - Add chicken thighs to the bowl, turning each piece to coat thoroughly with the marinade. Cover and refrigerate for at least 30 minutes, or up to 4 hours for deeper flavor penetration.
03 - Preheat oven to 400°F. Line a baking tray with parchment paper or aluminum foil for easy cleanup.
04 - Remove chicken from marinade, shaking off excess liquid. Arrange thighs on the prepared baking tray in a single layer, ensuring pieces are not touching for even roasting.
05 - Roast for 25 to 30 minutes, or until chicken is cooked through with an internal temperature of 165°F and edges are nicely caramelized.
06 - Transfer chicken to a serving platter. Sprinkle with toasted sesame seeds and sliced spring onions if desired. Serve immediately while hot.