If you haven't already, remove any excess meat from the turkey bones. You can leave some meat on for flavor if you prefer.
Chop the carrots, celery, and onion.
Smash the garlic cloves.
Place the turkey bones, chopped vegetables, smashed garlic, bay leaves, and optional herbs into the slow cooker.
Add the apple cider vinegar. The acidity helps draw out the nutrients from the bones.
Pour in 10 cups of water, or enough to cover all the ingredients in the slow cooker.
Set the slow cooker to low heat and cook for 12 hours. Cooking the broth slowly on low heat allows the flavors to meld and the nutrients to fully extract from the bones.
Once the broth has finished cooking, use tongs or a slotted spoon to remove the larger pieces of bones and vegetables from the slow cooker.
Carefully strain through a fine mesh strainer or cheesecloth into a large bowl or pot.
Season to taste.
Allow the broth to cool to room temperature before transferring it to storage containers. Store the broth in the refrigerator for up to a week, or freeze it for longer-term storage. Be sure to leave some space at the top of the containers if freezing, as the broth will expand as it freezes.
