Put your largest, tallest stockpot on over medium heat. Add vegetable oil.
Add mirepoix (carrots, onions, celery) to oil. Sauté for 2-3 min or until slightly softened. Add garlic and peppercorns. Add chicken bones and parts (frozen is fine). Add vinegar. Add at least enough water to cover 2 inches above ingredients. Add bay leaves and herbs.
Bring pot to a boil. Leave partially covered and turn down to a simmer. Simmer for a minimum of 3 (preferably 4-6) hours. If desired, skim debris periodically from surface of stock.
Taste stock. Add salt if desired (only if using for broth/soup base). Remove bones and strain through fine mesh strainer or colander lined with cheesecloth/double layer paper towels.
Cool stock, preferably in ice bath in sink. Cover and refrigerate overnight if not using immediately. On the following day, remove fat layer that forms on top of stock and discard.