01 - Place chicken bones into a large stockpot or Dutch oven.
02 - Add quartered onion, chopped carrots, celery, halved garlic, and sliced ginger to the pot.
03 - Pour in 12 cups of cold water, then add bay leaves, peppercorns, sea salt, and apple cider vinegar if using.
04 - Bring the mixture to a gentle boil over medium-high heat, then immediately reduce to a very low simmer. Skim off any foam or impurities during the first 30 minutes.
05 - Simmer uncovered for 4 hours, occasionally skimming foam and adding water if necessary to keep bones submerged.
06 - In the last 30 minutes of cooking, add fresh thyme and parsley if desired.
07 - Remove from heat and carefully strain broth through a fine-mesh sieve or cheesecloth into a large container, discarding solids.
08 - Taste and adjust seasoning. Let cool, refrigerate, and skim off any solidified fat before use.