Preheat the oven to 425°F. Lightly oil a roasting pan. Place in the prepared pan and roast for 15 minutes:
      5 pounds beef bones, preferably knucklebones
Add:
      2 medium onions, halved
      2 carrots, peeled and halved
      2 celery stalks, cut into 4-inch pieces
Roast, stirring occasionally to prevent the vegetables from burning, until the bones are well browned, about 40 minutes. Transfer the meat and vegetables to a stockpot, carefully pour off any excess grease without discarding the caramelized cooking juices, and add to the hot roasting pan:
      2 cups cold water
Scrape up any browned bits, then add the liquid to the pot along with:
      14 cups water (or just enough to cover)
Bring to a boil over medium heat, skim off the impurities, reduce the heat, and simmer gently. Skim often until impurities no longer appear, about 30 minutes. Add:
      1 leek, split lengthwise, cleaned thoroughly, and cut into 4-inch pieces
      1 bouquet garni, including 1 whole clove
Simmer, uncovered, for 8 hours, skimming as necessary and adding water as needed to cover. Strain into a clean pot or heatproof plastic container. Let cool, uncovered, then refrigerate. Remove the fat when ready to use.