4 pounds beef bones, preferably a mix of marrow bones and bones with a little meat on them, such as oxtail, short ribs, or knuckle bones (cut in half by a butcher)
2 medium unpeeled carrots, cut into 2-inch pieces
1 medium leek, end trimmed, cut into 2-inch pieces
1 medium onion, quartered
1 garlic head, halved crosswise
2 celery stalks, cut into 2-inch pieces
2 bay leaves
2 tablespoons black peppercorns
1 tablespoon cider vinegar
6-quart (or larger) stockpot or a large slow cooker