Preheat oven to 400°F (204°C). Spread bones on a roasting pan and roast for 1 hour, turning them halfway through.
Using tongs, transfer the roasted veal bones to a large stock pot. Pour 1.5 gallons of cold water over the bones.
In the same roasting pan, cook the vegetables over medium heat for 10 minutes. Add tomato paste and cook for an additional 5 minutes to caramelize, then transfer to the stock pot.
Pour the remaining 0.5 gallon of water into the roasting pan. Use a metal spatula to scrape up all the browned bits (the fond). Pour this liquid into the stock pot.
Bring the stock to a gentle simmer. Add the thyme, parsley stems, bay leaves, and black peppercorns. Cook over a gentle simmer for 10-12 hours.
Remove the bones using a spider or tongs. Then, strain the remaining stock through a fine-mesh strainer set over a bowl.
Pour the stock into containers to cool to room temperature. Then, transfer to the refrigerator for 1-2 days until a solid fat cap forms on top.
Peel the hardened fat cap off the top of the stock.