Preheat your oven to 375℉ (190ºC).

In a small bowl, mix the olive oil, salt, and pepper together.

Place the beef bones on a large baking pan and brush all sides generously with the olive oil mixture.

Roast the beef bones in the oven for one hour, flipping them halfway through.

Remove the bones from the baking pan and add them to your slow cooker along with the apple cider vinegar and filtered water.

Place a lid on the slow cooker and simmer your broth on low for 24 hours.

Ensure that the ingredients in your slow cooker are always submerged under the liquid. You can add more water if needed to keep them covered.

During the last hour of simmering, add the mushrooms, carrots, celery stalks, garlic cloves, rosemary, and bay leaf to the broth. Cover the slow cooker and continue simmering for the remaining time.

Let the broth cool enough to handle and remove the large pieces of bone and vegetables from the broth with a slotted spoon making sure to let any liquid drain back into the slow cooker.

Let the broth come to room temperature and transfer to the fridge to cool. Once your broth has cooled, a layer of fat will form at the top of your container. If desired, you can remove the fat cap and then use or store your bone broth.