To begin the stock, heat a large stock pot over medium-high heat and add a bit of oil. Once hot, add the roasted vegetables, along with the tomato paste and sauté for a couple of minutes. Turn off the heat and check on the bones.
Once the bones are nicely caramelized, add them to the stock pot. Discard the excess fat from the roasting pan. Place the pan over medium-high heat and deglaze with the red wine. Make sure to scrape up the bits from the bottom of the pan and move the pan around to help the wine reduce. Once the wine has reduced to a syrupy consistency, pour it into the stock pot.
Add enough cold water to cover the bones and vegetables by at least 2 to 3 inches. Bring everything to a simmer over medium heat, skimming off the impurities as they rise to the surface. Let the stock gently simmer for approximately 8 to 10 hours, skimming and adding more cold water, as needed to keep the bones covered.
About 30 minutes before the stock is finished, you can add the bouquet garni. While the stock simmers, skim off any fat or foam that accumulates on the surface.
Cook the stock for approximately 9 hours. To strain the stock, gently lift out the solids using a slotted spoon or spider. You can also use a large sieve (also known as a china cap) to scoop out the bones and vegetables.
Once all of the bones and vegetables have been removed, allow them to cool before discarding.
If the pot is too heavy, you can use a small sauce pan to help strain the remaining stock through a fine sieve. At this point, you are left with a beautiful veal stock. You can either skim off the excess fat now or you can refrigerate it and let the fat solidify.
If you do refrigerate the stock, for food safety reasons, you must cool the stock first. Place the pot into a sink full of ice and water and stir it from time to time until completely cooled. Transfer to the refrigerator.
After refrigeration, the fat will solidify on the surface and the stock itself will become gelatinous. Simply remove the fat from the top and discard.
You now have a flavorful dark veal stock, which can be used in many dishes.