Optional: Partially crush the peppercorns. Add whole black peppercorns to a mortar and pestle. Using the pestle, pound until 50% of the peppercorns are crushed or cracked into half. Or, add peppercorns to a ziploc baggie. Bash with a rolling pin until 50% crushed. (You can also skip this step and leave the peppercorns whole. Or use freshly cracked black pepper.)
Prep garlic. Separate an entire head of garlic, about 8-10 cloves. Smack each papered clove with the back of a knife -- it should crack the garlic cloves into pieces. Remove the papery peels. Roughly chop the garlic. You'll want big chunks.
Saute aromatics. Heat a large stockpot over medium heat. Add 1-2 Tbsp oil and swirl to coat the bottom of the pot. Add the crushed peppercorns, chopped garlic, and bay leaves. Stir with a wooden spoon until fragrant and the garlic is lightly golden, about 2 minutes.
Brown chicken. Add the chicken drumsticks. Stir until lightly browned all over, about 2-3 more minutes. Watch the garlic carefully so it doesn't burn.
Cook chicken. Add the vinegar, soy sauce, dark soy sauce, and sugar. Stir to combine. Cover with a lid and bring to a boil. Lower heat and simmer on medium-low. Cook (covered) until the chicken is tender and saucy, about 25 minutes. From time to time, stir and flip the chicken so all the sides are cooked evenly in the sauce.
NOTE: There is no need to add additional water, as the dish will release a lot of liquid as it cooks.
Serve. Transfer the Chicken Adobo to a shallow bowl. Make sure to scrape all the sauce into the serving dish! The chicken and sauce should be served together. Serve with white rice and make sure to pour the sauce over the rice! Steamed green veggies made a nice addition.