In a wide bowl, whisk soy sauce, vinegar, garlic, bay leaves, peppercorns, sugar, and water. Nestle the chicken thighs skin-side up, cover, and marinate at least 30 minutes—or up to overnight in the fridge for deeper flavor.

Heat oil in a large Dutch oven over medium heat. Remove chicken from marinade (reserve liquid), and sear skin-side down until golden, about 4 minutes. Flip and brown the other side 2 minutes. Transfer to a plate.

If using onion, add slices to the pot and cook until soft, about 3 minutes, stirring to pick up browned bits. Those bits jam-pack flavor.

Return chicken to the pot, pour in leftover marinade, and bring to a gentle boil. Scrape any fond from the bottom with a wooden spoon.

Lower heat to maintain a bare simmer, cover partially, and cook 30–35 minutes, turning chicken halfway. The sauce should reduce by about one-third and thicken lightly.

For a crunchier finish, remove the lid, increase heat to medium-high, and cook 3–5 more minutes until sauce clings to the chicken and skin crisps.

Pierce the thickest part of a thigh—juices should run clear. Adjust seasoning: add a pinch of sugar if too tangy or a splash of vinegar if too mellow.

Let the chicken rest 5 minutes off the heat. Serve over steamed jasmine rice, garnish with chopped green onions or toasted sesame seeds for extra flair.