Preheat the oven to 400°F.  Chop the turkey wings into sections at the joints with a cleaver or a heavy knife, place in a large roasting pan and roast, turning occasionally, until golden brown, about 1 hour.

Meanwhile, heat 2 Tbs. vegetable oil (not olive oil) in a large pot over medium-high heat, add the onion, carrot, and celery with leaves.  Cook, stirring occasionally, until softened, about 15 minutes.  Add the browned turkey wings to the pot.

Add to cups of water to the roasting pan, place on the stove top over high heat, and bring to a boil.  Scrape up all the browned bits in the pan with a straight-edged wooden spoon, and pour the water into the pot with the turkey and vegetables.  Add enough cold water to cover the turkey and vegetables by 2 inches and bring to a boil, skimming off the foam that rises to the surface.  Once the stock has come to a boil, reduce the heat to low.  When there is no more foam on the surface, add the parsley sprigs, thyme, and peppercorns.  Simmer uncovered until full-flavored, 3-4 hours.

Strain the stock into a large bowl, discarding the solids from the strainer.  Let cool a bit, then refrigerate uncovered until chilled.  When ready to use, skim the fat from the surface and discard.  If all has gone well, the cold stock will be gelatinous, not liquid-y.