01 - Place the beef bones in a large stockpot or slow cooker. For deeper flavor and richer color, roast the bones beforehand at 400°F for 30 minutes.
02 - Add the carrots, celery, onion, garlic, bay leaves, parsley, and peppercorns to the pot with the bones.
03 - Pour in the apple cider vinegar and cold water, ensuring the bones and vegetables are completely submerged.
04 - Bring the mixture to a gentle simmer over medium heat. During the first hour, skim off any foam or impurities that rise to the surface using a skimmer or ladle.
05 - Lower the heat and simmer uncovered or partially covered for at least 12 hours. Occasionally add water as needed to keep the bones submerged throughout the cooking process.
06 - Strain the broth through a fine-mesh sieve or cheesecloth, discarding all solids. Season the finished broth with salt to taste.
07 - Allow the broth to cool completely. Refrigerate to let the fat solidify on the surface, then skim off if desired. Store in the refrigerator for up to 5 days or freeze for up to 3 months.