Preheat the oven to 350°F (180°C).
Put the bones, shanks, onions, thyme, bay leaves, and garlic in a roasting pan. Pour some oil over everything and toss. Roast until the bones are lightly colored. Transfer everything to a large soup pot. Pour in at least 4 quarts (4 L) water and add the remaining ingredients except the salt and ground pepper. Bring to a boil. Lower the heat and let the stock reduce over very low heat for about 3 hours. Occasionally, skim the foam off the stock with a skimmer. If you don’t do it, your stock will become cloudy. Sieve the stock or pour it through a colander in which you’ve placed a clean kitchen towel. Let cool. Put the stock in the fridge. Skim off the congealed fat as soon as the stock is cold. Season the stock with salt and pepper. I often add some Worcestershire sauce and sometimes some salty soy sauce, so the stock develops a richer flavor and color.