1Combine the marinade ingredients. In a large bowl, mix together the soy sauce, vinegar, water, crushed garlic cloves, bay leaves, and whole black peppercorns. Add the chicken pieces and turn to coat thoroughly in the marinade. For best flavor, cover and refrigerate for at least 30 minutes, or up to overnight - the longer the marination, the more deeply the flavors will penetrate the chicken. If short on time, you can skip marinating and proceed directly to cooking, though the flavor will be less intense.
2Remove the chicken from the marinade, reserving all the liquid, garlic, and aromatics. Pat the chicken pieces dry with paper towels - this step is important for achieving a good sear. Heat the vegetable oil in a large Dutch oven or heavy-bottomed pot over medium-high heat until shimmering. Working in batches to avoid overcrowding, add the chicken pieces skin-side down and sear for 3-4 minutes until the skin is golden brown and releases easily from the pan. Flip and sear the other side for 2-3 minutes. Transfer the browned chicken to a plate.
3Pour off all but about 1 tablespoon of fat from the pot. Add the reserved garlic cloves and cook over medium heat for 1-2 minutes until fragrant and lightly golden - do not let them burn. Pour in the reserved marinade (soy sauce, vinegar, water, bay leaves, and peppercorns), scraping up any browned bits from the bottom of the pot. These fond bits add tremendous flavor to the final sauce.
4Return the browned chicken pieces to the pot, nestling them into the liquid. The chicken should be about halfway submerged - add a splash more water if needed. Bring the liquid to a boil, then reduce heat to low, cover the pot, and simmer gently for 30-35 minutes. Turn the chicken pieces occasionally to ensure even cooking and flavor absorption. The chicken is done when it is very tender and the meat pulls easily from the bone. An instant-read thermometer inserted into the thickest part should read at least 175 degrees F for dark meat.
5At this point, you can choose your preferred adobo style. For saucy adobo: remove the chicken to a serving plate and keep warm. Increase heat to medium-high and simmer the sauce for 5-8 minutes until reduced by about half and slightly thickened. Taste and add the brown sugar if you prefer a slightly sweeter, more balanced sauce - this is optional and a matter of personal preference. For dry adobo: remove the lid and continue simmering the chicken in the sauce, turning occasionally, until the liquid has almost completely evaporated and the chicken is coated in a sticky, caramelized glaze. This method produces crispier, more intensely flavored chicken.
6Transfer the chicken to a serving platter. If you made saucy adobo, pour the reduced sauce over the chicken, including the softened garlic cloves - they are delicious and should be eaten. Fish out and discard the bay leaves. Garnish with sliced green onions. Serve immediately over steaming hot white rice - jasmine rice is traditional and perfect for soaking up the savory sauce. Many Filipinos consider the sauce-soaked rice to be the best part of the dish. Adobo actually tastes even better the next day after the flavors have melded further, and it reheats beautifully. Store refrigerated for up to 4 days. The fat may solidify on top when cold - simply reheat and it will melt back into the sauce.