Preheat over to 450°F. Place beef bones, carrots, leek, onion, and garlic on a roasting pan or rimmed baking sheet and roast for 40 minutes, stirring halfway.
Fill a large slow cooker with 12 cups of filtered water.
Next, add celery, bay leaves, peppercorns, and vinegar to the pot of filtered water.
Add the roasted bones and vegetables into the pot along with any juices.
Add additional water as needed to cover bones and vegetables.
Cook the bone broth on low for 8 - 24 hours (the longer the better).
Let the bone broth cool slightly and strain the bones and vegetables.
Refrigerate in airtight mason jars until fat is solidified on the top of the broth.
When ready to use, scrape excess fat and warm the broth on low heat until it is liquid consistency.
Add sea salt and fresh herbs to taste.