Preheat the oven to 425°F.
Spread the bones in a roasting pan in a single layer and roast for about 30 minutes, turning once, until well browned.
Remove from the oven and paint a thin layer of tomato paste over the bones — this deepens the color and flavor of the finished stock.
Pile the vegetables on top of the bones and roast another 15–20 minutes, until they caramelize.
Transfer the bones and vegetables to a stockpot.
Deglaze the roasting pan with the wine (or water), scraping up the browned bits, and pour it into the stockpot.
Add the peppercorns, bay leaves, and thyme. Cover the bones with cold water — about 5 to 6 quarts for 7 pounds of bones, or enough to cover them by roughly an inch
Over medium heat, bring the pot slowly up to a bare simmer. Don't let it boil.
Adjust the heat to hold a gentle bubble, and skim off any foam every 30 minutes.
Let the stock simmer for at least 4 hours, up to 12 if you have the time. Top off with more water if it's evaporating faster than it should.
When it's done, remove and discard the bones. Strain through a fine mesh strainer, or a colander lined with three or four layers of cheesecloth, for a clear stock.
Chill quickly — portion it into smaller containers first, since smaller volumes cool faster and more safely than one large pot. Refrigerate, then skim off the solidified fat from the top and discard.