Place chicken bones in a large stockpot or slow cooker.
Add onion, carrots, celery, garlic, and bay leaves.
Pour in apple cider vinegar and water, ensuring bones are fully submerged.
Heat the mixture until it reaches a gentle boil, then lower the heat to maintain a simmer.
Simmer for 8 hours, occasionally skimming off any foam or impurities.
Strain the broth using a fine-mesh sieve and dispose of the solid ingredients.
Season with salt and pepper to taste. Serve warm or store for later use.