If the bones are raw, roast them in the oven for 30 minutes at 350 degrees F.
Place bones in a large stock pot. Pour cold water over the bones. Add vinegar. Let sit for 25 minutes.
Meanwhile, rough chop the onion, carrots and celery. Add to the pot along with the salt and peppercorns.
Bring to a vigorous boil then reduce to a simmer. Simmer for 4 hours. Remove any impurities that float to the top. Scoop off the foamy layer on the top.
After 4 hours add the garlic and parsley. Simmer for another 45 minutes.
Remove from heat and let cool slightly. Strain using a fine strainer to remove the bones and vegetables. Store in the fridge for up to a week or freeze for later use.