Ingredients
3 to 4 pounds mixed beef bones, short ribs, oxtails, knuckles, and neck bones (see Recipe Note)
1 tablespoon olive oil
2 medium carrots
3 stalks celery
2 medium yellow onions
2 tablespoons cider vinegar
1 bay leaf
Extra flavoring ingredients: fresh ginger, fresh or dried mushrooms, fish sauce, garlic, fresh or dried herbs

Equipment
Baking sheet
Tongs
Chef's knife
Large stock pot, 6-quart slow cooker, or 6-quart pressure cooker (or larger)
Strainer
Cheesecloth (optional)