In a large bowl or zip-top bag, combine the chicken, soy sauce, cane or coconut vinegar, smashed garlic, bay leaves, and whole black peppercorns. Mix well and marinate for at least 30 minutes, ideally overnight.

Heat cooking oil in a large pot over medium-high heat. Pat the marinated chicken dry and sear in the hot oil for about 3–4 minutes on each side until golden brown. Transfer to a plate and set aside.

In the same pot, sauté the sliced onion for 2–3 minutes until translucent. Return the browned chicken to the pot and stir to combine.

Pour in the reserved marinade and 1 cup of water, add brown sugar if using. Bring to a boil, then reduce to simmer uncovered for 30–40 minutes. Stir occasionally.

Once tender and the sauce thickened, adjust seasoning with salt and ground black pepper. Discard bay leaves and serve hot over steamed rice, garnished with scallions or fried garlic.