Step 1Heat the oven to 425 degrees. Place the bones in a large roasting pan and roast until brown, about 2 hours.
Step 2Meanwhile, make a bouquet garni by placing the parsley, thyme and bay leaf inside the leek halves and tying them with kitchen twine, leaving one end of the string about 24 inches long.
Step 3Remove the bones from the oven; put into a very large (20-quart) stockpot. Add 10 quarts cold water and heat uncovered over medium heat until the liquid comes to a simmer, about 40 minutes. Reduce the heat to low and simmer very gently uncovered for about 8 hours, occasionally skimming the top to remove scum and being very careful not to let the stock boil. (If the stock boils even at the lowest heat, move the pot slightly to one side.)
Step 4Meanwhile, pour off the fat from the roasting pan and reserve. Add the chopped onions, celery and carrots and about 2 tablespoons of the reserved fat (enough to coat the vegetables, discarding the rest of the fat), spreading the vegetables evenly. Return the pan to the oven and roast about 1 hour, until very caramelized but not burnt, stirring after 30 minutes.
Step 5Remove the roasting pan from the oven and put it on the stovetop. Over medium-low heat on two burners, add the tomato paste and cook for about 2 or 3 minutes, stirring to combine and prevent scorching. Add the vegetable mixture to the stockpot.
Step 6Reduce the heat under the roasting pan to low, add the wine and deglaze, scraping up the browned bits. Pour the contents of the roasting pan into the stockpot. Add the peppercorns and the bouquet garni, tying the twine to the pot handle.
Step 7After 8 hours strain the stock into a large stockpot through a large fine-mesh strainer. Put the pot with the stock in the sink, and add ice cubes and cold water to the sink so the stock cools quickly. Cool, cover and refrigerate.
Step 8When the stock is cold, remove and discard the layer of fat from the surface. Refrigerate or freeze the stock until needed.