01 - Place the chicken bones into a 6–8 quart slow cooker, distributing them evenly across the bottom.
02 - Layer the roughly chopped carrots, celery, quartered onion, and smashed garlic cloves over the bones.
03 - Tuck the bay leaves, whole peppercorns, fresh parsley, and thyme sprigs into the mixture.
04 - Pour in the apple cider vinegar and cold water, ensuring all solids are fully submerged beneath the liquid.
05 - Set the slow cooker to LOW and cook for 12 to 18 hours, skimming off any foam that rises to the surface periodically.
06 - Pass the finished broth through a fine-mesh sieve or cheesecloth into a large bowl. Discard all spent solids.
07 - Stir in salt to taste. Allow the broth to cool, then skim off and discard any solidified fat from the surface if desired.
08 - Transfer the broth to airtight containers or jars. Refrigerate for up to 5 days, or freeze for extended storage.