Step 1: In a bowl, combine the chicken, soy sauce, garlic, and bay leaves. Mix well and let it marinate for at least 30 minutes (or up to overnight in the refrigerator for deeper flavor).
Step 2: In a large pot, heat the oil over medium heat. Add the onion and sauté for 5 minutes or until translucent.
Step 3: Remove the chicken from the marinade and add it to the pot. Reserve the marinade for later. Sear the chicken pieces until they are lightly browned on all sides, about 7 minutes.
Step 4: Pour in the reserved marinade, along with the vinegar and water. Add black peppercorns, if using. Bring to a boil, then reduce the heat to low. Simmer uncovered for about 40 minutes, or until the chicken is tender and fully cooked. Add sugar and allow to dissolve.
Step 5: Prepare rice according to package directions.
Step 6: Taste the sauce and adjust the seasoning with salt and pepper as needed. For a thicker sauce, simmer longer to reduce it.
Step 7: Serve the chicken adobo hot over steamed rice, spooning the sauce over the top.