Put garlic, ginger, honey, soy sauce, and sherry in a blender and process for 30 seconds. Pour this marinade into a 9x13-inch baking pan and then put chicken thighs in pan, coating well. Cover and refrigerate for at least 2 hours.
Line a cast-iron skillet with aluminum foil and sprinkle brown sugar and tea on top of the foil. Place a wire rack in the skillet and place the chicken on top.
Cover with lid and cook chicken on medium-high heat for 30 minutes - WITHOUT lifting the lid! Sprinkle chicken with sesame seeds and serve with peanut or hot mustard sauce.