Step 1

To make the crust: Combine the flour, buttermilk powder, salt, and baking powder, then mix in the butter and shortening until crumbly, leaving some pea-sized lumps., Mix the vinegar with 4 tablespoons of the water. Sprinkle onto the dry ingredients, stir, and squeeze the dough together; if it's not totally cohesive, add an additional tablespoon of water (enough to make the dough stick together nicely, without crumbling)., Shape the dough into a flattened disk, wrap it in plastic wrap, and refrigerate for 30 minutes., To make the filling: In a saucepan set over medium heat, melt the butter, then stir in the flour. Gradually pour in the stock, whisking constantly. Cook and stir the sauce until it comes to a boil, then reduce the heat and simmer for 5 minutes., Stir in the chicken and salt. Add ground black pepper, additional salt to taste, and the vegetables., To assemble and bake the pie: Spoon the filling into a 9" or 10" deep-dish pie pan.

Step 2

, Roll the crust out slightly larger than the pan. Place it on top of the filling; cut several vent holes, and use any scraps of dough to decorate. Place the pie on a baking sheet (there may be some drips once the filling begins to bubble),, Bake the pie in a preheated 375°F oven for 40 to 50 minutes, until the crust is golden brown and the filling is bubbly., Remove the pie from the oven and let it cool for about 20 minutes before serving. This short rest gives the filling a chance to set, making it easier to cut and plate.

Step 3

, Store any leftover pie, securely wrapped, in the refrigerator for several days; freeze for longer storage.