Mix the Marinade: In a small bowl, whisk together the miso paste, soy sauce, mirin, sake, brown sugar, and minced garlic.
Marinate the Chicken: Place chicken thighs in a zip-top bag or shallow dish, pour the marinade over them, and massage it in. Refrigerate for at least 30 minutes.
Sear the Chicken: Heat a large skillet over medium-high heat with vegetable oil and sesame oil. Sear each side of the chicken for about 4-5 minutes until golden and crispy.
Finish Cooking: Lower the heat, pour in any leftover marinade, and let the chicken cook through for another 8-10 minutes, basting occasionally.
Rest and Serve: Take the chicken off the heat, let it rest for 5 minutes before slicing, and serve hot.
