Chicken/lamb/beef bones/carcass/legs/feet - ideally sourced from your butcher and grass fed/organic (if not, from your local supermarket is fine)
Enough water to well cover all ingredients
Onion, celery, carrots, and other non-starchy vegetables (skin and all)
2 tbsp Apple cider vinegar
Simmer for 6-12 hours (at a low heat) in either a slow cooker/crockpot or in a large pot on the stove top. The longer you can boil the broth the more nutrients will be released from the bones and meat. You will find a longer cooking period will elicit a broth which is gel-like in consistency when cool (that's good).
Save all of your vegetable off-cuts over the week and use in your weekly stock. This is a great way to recycle you vegetable scraps.