Mix the corn starch with water in a small bowl until the corn starch is fully dissolved. Next, add all the rest of the marinade ingredients and mix until combined.
Assemble the dish:
Place the thighs, potatoes, onion, and garlic into a baking dish and mix thoroughly with the marinade, making sure that the chicken thighs are marinated well. *Optional* sprinkle with fresh herbs.
Cover the dish with foil and bake for 50-60 minutes.
Remove the foil, and turn on the broiler. Broil for 5-10 minutes, constantly watching, until lightly browned. Pull them out of the oven as soon as they reach the desired color (internal temperature 165°F/73°C).
Serve warm.