In a roasting pan, arrange the veal bones in a single layer, then drizzle with oil and season with salt and pepper. Roast the bones in the lower part of the oven, flip after 20 to 30 minutes and remove from the oven after 40 minutes to 1 hour, when the bones are golden brown.
Smear the tomato paste over the bones with a spoon. Add the carrots, celery, onion, leeks, and garlic. Return to oven and roast for 1 additional hour.
Into a large stockpot, add the roasted bones, roasted vegetables, thyme, rosemary, and parsley and 16 cups of water. Discard fat from roasting pan. Place roasting pan directly onto stovetop and heat on medium for 1 minute. Remove from heat and immediately add 1/2 cup to 1 cup of water to the roasting pan, scraping up the brown bits. Add the deglazed liquid to the stockpot. Bring the liquid to a tremble (190 degrees F), and simmer for 8 hours, skimming and discarding the froth frequently during the first hour.
Pour the stock in batches through a large fine sieve and discard the solids. Skim off the fat. (Alternatively, cool the stock, uncovered, and chill, covered. Scrape away and discard congealed fat from the chilled stock.) Gently simmer the stock, skimming the froth occasionally, until it is reduced to about 4 cups, about 1 hour. Before storing the stock cool it completely, about 1 hour, uncovered. Stock keeps, 1 week when covered and chilled or, 3 months when frozen in airtight containers,
Cook's Note: If desired, pour the cooled stock into ice-cube trays and freeze. Frozen cubes keep 3 months in heavy-duty resealable plastic bags. Stocks are key to any restaurant as they are the base of so many recipes. When you go to cooking school, learning how to make stocks is one of the first things you do. Although this might seem laborious when you can just go to the grocery store and get one out of a box, there is nothing better than a homemade stock to add that extra depth to anything you might be making, whether it's a soup, a sauce, a braise or a roast. Just pick a rainy day when you have some stuff to do around the house, get your ingredients and go for it! You won't regret it. The best part about this is that you can freeze it in containers and use it for up to three months. Time very well spent. Not to say that grocery store stocks are bad, they do the job and if you really don't have the time, it's a great alternative.
When roasting the bones, you'll know it's time to add the vegetables when they're an irresistible golden brown color, almost caramelized by the glistening fat. You can't get any better than that!