4 pounds of beef bones — can include a mix of marrow bones and bones with meat
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
2 celery stalks, cut into 2-inch pieces
2 bay leaves
2 tablespoons black peppercorns
1 tablespoon apple cider vinegar
Preheat the oven to 450°F. Place beef bones, carrots, leek, onion, and garlic on a roasting pan. Roast for 40 minutes, tossing bones and vegetables once halfway through.
Fill a large stockpot with 12 cups of water. Add celery, peppercorns, bay leaves, and vinegar. Scrape bones and vegetables into the pot. Add water to cover ingredients if needed.
Cover the pot and bring to a low simmer. Open the lid slightly, and skim the foam occasionally for the next 8-to-24 hours. The longer you simmer, the richer the flavor. A slow cooker works just as well.
Remove pot from heat and let cool. Strain broth with a fine-mesh sieve, tossing out the bones and vegetables.
Store in a fridge for up to 5 days or the freezer for up to 6 months.