Preheat oven to 230ºC . Put the oil in a roasting pan and heat briefly in the oven. Add the bones to the oil in the pan, toss to coat and roast for 35 minutes.
Add the onions, carrots, celery, leek, garlic and parsley, tossing them all to coat with fat. Roast 30 minutes longer. Remove the pan from the oven and transfer the bones and vegetables to a clean stockpot. Drain off as much of the fat as possible. Place the roasting pan over medium-high heat (use 2 burners if necessary), and add 2 cups of cold water and boil briefly. Scrape up all of the browned bits into the water. Transfer the liquid to the stock pot and add enough cold water to cover. Bring slowly to a boil, skimming off all of the froth that forms. Lower the heat and add tomatoes, thyme, bay leaves, cloves and salt. Simmer uncovered for 6 to 8 hours adding water as necessary just to cover the ingredients. Skim whenever necessary. Add peppercorns for the last 15 minutes of the simmering. Strain the "soup" into a large bowl through a colander lined with a double layer of dampened cheesecloth. Gently press the solids to extract all of the liquid, and discard the solids. Pour the stock into containers for storage and label and date them. The stock will "keep" for up to 3 days in a refrigerator, and up to 6 months in a freezer.