01 - Place the chicken bones in the bottom of a 6 to 8 quart slow cooker.
02 - Layer the roughly chopped carrots, celery, quartered onion, and smashed garlic cloves over the bones.
03 - Tuck the bay leaves, whole peppercorns, parsley, and thyme sprigs into the mixture.
04 - Pour in the apple cider vinegar and cold water, making sure all the bones and vegetables are fully submerged.
05 - Cover and cook on LOW for 12 to 18 hours, skimming off any foam that rises to the surface as needed.
06 - Carefully strain the finished broth through a fine-mesh sieve or cheesecloth into a large bowl. Discard all solids.
07 - Stir in salt to taste. Allow the broth to cool completely, then skim off and discard any solidified fat from the surface if desired.
08 - Transfer the cooled broth to airtight containers or jars. Refrigerate for up to 5 days, or freeze for longer storage.