01 - Place chicken bones, onion, carrots, celery, garlic, and sliced ginger into a large stockpot or Dutch oven.
02 - Pour in cold water to fully submerge the ingredients and add bay leaves, black peppercorns, sea salt, and apple cider vinegar if using.
03 - Bring the mixture to a gentle boil over medium-high heat, then reduce heat to maintain a very low simmer.
04 - During the first 30 minutes of simmering, skim off any foam or impurities that rise to the surface.
05 - Allow the broth to simmer uncovered for 4 hours, occasionally skimming and adding water to keep bones submerged.
06 - In the final 30 minutes of cooking, add fresh thyme or parsley if desired for added aroma.
07 - Remove from heat and carefully strain the liquid through a fine-mesh sieve or cheesecloth into a large bowl, discarding solids.
08 - Taste the broth and adjust seasoning as needed. Let cool, refrigerate, and skim off any solidified fat before use.