The night before, assemble the marinade. Combine soy sauce, Chinese cooking wine, water, garlic, 1/4 of an onion (diced), and sugar in a large pot and heat over low until sugar dissolves. Let cool.

Remove the skin from each chicken thigh if not already removed. Poke holes in the thighs using a fork.

Add the chicken thighs to the marinade and let them sit in the fridge overnight, turning the thighs partway through.

The next day, preheat the oven to 350°F.

Thinly slice the remaining 1 and 3/4 onions.

On a large, aluminum-foil-covered baking pan, arrange the onions evenly across. Gently squeeze the excess marinade out of each chicken thigh and arrange chicken thighs on top of the onions.

Bake at 350°F for 40-45 minutes, or until chicken thighs are fully cooked through.

Plate each chicken thigh with a side of roasted onions and enjoy!