Preheat oven to 375. Line a baking sheet with aluminum foil. Place beef bones on top of the foil and roast for 30 minutes.
Place carrots, celery, onion, bay leaves, salt, and pepper into bottom of a slow cooker and mix well. Place beef bones on top of the vegetables and add enough water to cover the bones. Stir in apple cider vinegar.
Place the lid on the slow cooker and cook on low for 12-14 hours. When cooking is complete, turn off slow cooker and let stand for one hour.
Use a slotted spoon to remove the bones and vegetables from the broth and discard.
Using 2 layers of cheesecloth wrapped around a large bowl, strain the broth into a separate bowl. Skim off the fat if desired. Let cool completely before storing covered in jars.