Step 1Heat the oven to 450 degrees. Place the bones in a heavy roasting pan and roast until darkened and aromatic, about 30 minutes.
Step 2Remove the bones and place in a large, heavy stock pot. Depending on how much fat is in the pan, add just enough oil so you have enough fat to brown the vegetables. Heat the pan on the stove-top over medium-high heat until hot. Add the onion, carrot and celery and cook, stirring frequently, until softened and browned, 10 to 12 minutes.
Step 3Reduce the heat and stir in the tomato paste, coating the vegetables. Continue to cook until the paste begins to darken and forms a film on the bottom of the roasting pan, careful not to burn. Off heat, carefully add the wine (it will steam), and stir it in with the vegetables, scraping any flavoring from the base of the pan.
Step 4Add the vegetables and the scraped flavoring to the stock pot. (If you still have some flavoring stuck to the pan, add a little water to loosen, then scrape into the pot). Add the leek leaf, along with the thyme and parsley sprigs, as well as the peppercorns. Add the garlic cloves, if using. Add the water.
Step 5Bring the mixture to a boil over high heat, then reduce the heat to a very gentle simmer. Skim the surface of the stock as needed, discarding the foam, impurities and fat that rise to the surface. Gently simmer the stock for 4 to 7 hours, adding water, if needed, to keep the bones covered.
Step 6Strain the stock through a fine sieve lined with cheesecloth (save the bones to make a remouillage, or second stock, if desired), discarding the solids. Cool the stock, then refrigerate until needed (be sure to remove and discard any fat that has solidified at the top of the stock before using).