Blanch the bones. Place in a stockpot and cover with cold water. Bring to a boil over high heat and simmer for 15-20 minutes before draining and rinsing the bones with water.
Roast the bones and the vegetables. Preheat the oven to 450 degrees Fahrenheit. Transfer bones to a roasting pan. Roast for 45 minutes.
Simmer the bones. Place the bones in a stockpot or crockpot and add the onion, garlic, carrots, celery, bay leaves, peppercorns, and apple cider vinegar. Fill it with approximately 12 cups of water, or until bones are fully submerged. Cover and bring to a low and gentle boil. Simmer for a minimum of 12 hours. Ideally 24-48 hours.
Strain the bones. Once the bones have simmered and your broth is ready, you will need to strain the broth through a fine mesh strainer. Set aside the broth to cool and allow the bones to cool.
Skim the fat from your broth (optional). Transfer broth to the refrigerator and allow the broth to cool fully. The result will be a hard, thick layer of fat and a bottom layer that is your bone broth (which should look like gelatinous brown jello). If desired use a fork to scoop off the top layer of fat. This will leave behind the healthy bone broth, minus the fat.
Finish the Soup. Return to the Stove, simmer for 15 minutes add mushrooms, and radish, and simmer for 5 minutes more. Turn off the heat and add scallions.
