01 - Arrange beef bones in a large stockpot or slow cooker. For deeper flavor, roast bones at 400°F for 30 minutes beforehand.
02 - Add carrots, celery, onion, garlic, bay leaves, parsley, and peppercorns to the pot with the bones.
03 - Pour in apple cider vinegar and cold water, ensuring all bones and vegetables are fully submerged.
04 - Bring to a gentle simmer over medium heat. Skim off any foam or impurities that rise to the surface during the first hour.
05 - Reduce heat to low and simmer uncovered or partially covered for at least 12 hours. Add water occasionally to keep bones submerged.
06 - Strain the broth through a fine-mesh sieve or cheesecloth. Discard all solids and season with salt to taste.
07 - Let cool completely, then refrigerate to allow fat to solidify on the surface. Skim off fat if desired. Store in the refrigerator for up to 5 days or freeze for up to 3 months.