Duck Stock: Preheat the oven to 450 degrees F. Lay the duck bones out on a sheet tray. Put the tray on the middle rack in the oven. Roast the bones until they are a deep golden brown, about 1 hour.
Drain any fat from the tray and put the bones in a stockpot. Add the remaining ingredients and bring to a boil over high heat. Reduce the heat to medium-low and simmer uncovered for about 3 hours. Skim off any fat that accumulates at the top with a ladle while it is simmering.
After 3 hours, strain the stock. You should yield about 2 quarts of stock, if you have ended up with much more continue to simmer it until reduced to 2 quarts. Set aside.
Duck Gravy Filling: Melt the butter over medium heat in a large saucepot. Do not let the butter brown. Whisk in the flour and cook over medium heat, stirring frequently, until it turns very light brown, about 5 minutes. Slowly whisk in 6 cups of the hot duck stock. Make sure to add the stock very slowly, whisking the entire time to avoid getting any lumps. Once it comes to a boil, reduce the heat to low and add all the remaining ingredients, except for the five-spice powder. Simmer until the gravy thickly coats the back of a spoon and the vegetables are tender, about 30 minutes. Season the gravy, to taste, with salt, pepper, and the five-spice powder.
Preheat the oven to 350 degrees F.
Assemble the potpie. Roll out 2 refrigerated pie crusts to about 13 inches in diameter. Lay 1 crust in a 9-inch deep-dish pie plate, making sure to have at least 1/2-inch extra hanging over the sides of the dish. Fill with about 1/2 of the potpie filling, or until the filling is just under the level of the top of the dish. Gently, lay the other crust over the top. Trim the edges of the crust with scissors so that you have only about 1/2-inch extra. Tuck the crusts under all around and crimp closed using a fork. Brush the top of the pie with the egg white. Cut 3 small slits in the center of the pie. Put the pie on a sheet tray and bake in the preheated oven until the crust is golden brown and the center is piping hot, about 1 hour.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.
Recipe courtesy of Jessica O'Donnell, Executive Chef at Good Dog Bar and Restaurant in Philadelphia, PA