Preheat the oven to 400ºF (200ºC). Arrange chicken bones in an even single layer on a baking sheet. Roast bones until browned, 1 hour.
1
Add bones and vegetables
Add the bones to a large stock pot or large Dutch oven. Add the onion, celery, carrot and garlic.
2
Cover with water
Cover with water (about 4 quarts of water) and add the parsley, bay leaves and peppercorns.
3
Simmer the stock
Bring to a boil over medium heat then lower the temperature and simmer, using a spoon to skim off any scum that rises to the surface and discard it.
4
Skim any scum
Continue to keep at a gentle simmer (just a few small bubbles) for about 6 hours, until reduced by about half. Add additional water as needed.
5
Strain stock
Once the stock is done, remove from heat and let cool. Use tongs to remove any large bones, then strain the stock through a fine mesh strainer into a large bowl, discarding solids.
6
Store stock
Let cool for about an hour then transfer the broth to storage containers or resealable plastic bags and refrigerate or freeze until ready to use.