01 - For deeper flavor and richer color, arrange beef bones on a baking sheet and roast at 400°F for 30 minutes before simmering. Transfer roasted bones to a large stockpot or slow cooker.
02 - Add the roughly chopped carrots, celery, quartered onion, smashed garlic cloves, bay leaves, fresh parsley, and whole black peppercorns to the pot with the bones.
03 - Pour in the apple cider vinegar and 12 cups of cold water, ensuring all bones and vegetables are fully submerged.
04 - Bring the mixture to a gentle simmer over medium heat. During the first hour, use a skimmer or ladle to remove any foam or impurities that rise to the surface.
05 - Reduce heat to low and maintain a gentle simmer, uncovered or partially covered, for at least 12 hours. Check periodically and add water as needed to keep the bones submerged.
06 - Carefully strain the broth through a fine-mesh sieve or cheesecloth into a large container. Discard all solids. Season the strained broth with salt to taste.
07 - Allow the broth to cool to room temperature, then refrigerate. Once chilled, the fat will solidify on the surface — skim off if desired. Store refrigerated for up to 5 days or freeze for up to 3 months.