Add all the ingredients into a slow cooker, turn the heat to high until it starts boiling. then reduce to medium heat and simmer for 24-48 hours. The longer you let it simmer the more nutrients will leach from the bone into the broth.
Strain the solids from the liquid and enjoy.
You can consume it directly or let it cool and skim the fat off the surface. The fat can later be used for frying or roast potatoes. Refrigerate the bone broth and consumed within 7 days or freeze for up to 3 month. If you freeze it in ice cube trays you can use it as single beef stock portions.