6 to 7 pounds elk, deer, or beef bones, knuckles and joints preferred
2 tablespoons olive oil, divided
4 carrots, scrubbed and halved
4 medium yellow onions, unpeeled, each quartered
3 celery ribs, halved
1 head garlic, halved
1/4 cup tomato paste
20 parsley stems
10 thyme sprigs
3 bay leaves
1/4 teaspoon whole black peppercorns
Preheat the oven to 475℉ degrees F.
Place the bones on a rimmed baking sheet and rub them with 1 tablespoon of the oil. Roast, flipping them halfway through, until they are deeply browned, 35 to 45 minutes.
Meanwhile, in a medium bowl, combine the carrots, onions, celery, garlic, tomato paste, and remaining 1 tablespoon oil. Toss well to coat the vegetables in the tomato paste. Transfer the roasted bones to a large stockpot. Spread the coated vegetables on the hot baking sheet and roast, tossing halfway through, until evenly browned, about 20 minutes.
Add the vegetables to the stockpot along with theparsley stems, thyme, bay leaves, and peppercorns. Place the rimmed baking sheet over medium heat and add enough water to cover the bottom of the pan. Carefully use a wooden spoon to scrape up the browned bits from the bottom of the pan. Add everything to the stockpot.
Fill the stockpot with enough cold water to cover the bones by a few inches, about 8 quarts. Bring to a simmer over medium heat, skimming off any foam that may rise to the surface as the mixture heats. Reduce the heat to low to maintain a very gentle simmer. Simmer the stock, uncovered, skimming off fat as needed, until the stock is very flavorful and reduced by a half, anywhere from 10 to 24 hours. Reserve the fat for croutons or for another use.
Strain the stock and cool it rapidly in a bowl set over an ice bath. The stock is now ready to use or can be stored in the refrigerator for up to 5 days or frozen for up to 3 months.