Place the bones in a single layer on a baking sheet or roasting pan; roast for 60 minutes, flipping each bone over half way through cooking time.
Meanwhile, roughly chop the vegetables (don't even bother peeling them) and place them, along with the bay leaf and apple cider vinegar into a 6 quart slow cooker. Add the bones as soon as they come out of the oven and then fill the pot completely with water.
Set the slow cooker on low, cover and cook for 18 to 36 hours, or until the broth has reached a beautiful brown color and has filled the house with the most intoxicating aroma.
Carefully remove the larger pieces with a slotted spoon and place them in a strainer set over a large bowl to collect the excess broth. Then, strain the broth that's still in the crockpot through a fine meshed sieve, or through a strainer that's been lined with cheesecloth.
Transfer the bone broth into jars and refrigerate promptly. The fat will float to the surface and form a protective barrier that will prevent air from getting in contact with your broth.
Once the broth has fully cooled, you'll be able to to remove some or all of that fat layer of fat that formed at the top, which you'll then be able to use for cooking.