Roast bones: Preheat oven to 200 degrees Celsius/ 400 degrees Fahrenheit. Place the beef bones in a single layer on a roasting pan. Drizzle with the oil and rub the bones to coat with it. Roast for 30 minutes, then flip the bones over and roast for an additional 30 minutes.
Simmer: Put bones, bay leaf, cider vinegar, chopped vegetables, and peppercorns in a large crockpot or soup pot. Cover entirely with water and bring almost to a boil, but don't let it start to boil. Add salt. Turn the heat down to low and let simmer for 12-24 hours. If using a crockpot/slow-cooker, simmer on Low for 12-24 hours. Add water, if necessary, to keep all the ingredients submerged.
Strain: Once the broth has reached a dark rich brown color, remove from heat. Discard the bones, vegetables, and bay leaf and strain through the bone broth through a fine-meshed sieve lined with a cheesecloth into a clean pot.
Store: Once at room temperature, pour into jars. Add more salt to taste when using the broth.
Skim the fat off the top of the broth before using it. Use as suggested above.