Make your pie dough. Take chilled butter, cube, place on plate and return to fridge. Measure out shortening and also put in fridge to chill. In a cup or small bowl, mix water with some ice.
Meanwhile, add flour and salt in a food processor with the s-blade. Pulse a few times to mix. Take butter and shortening out of the fridge and add to food processor. It's very important that they are chilled!
Pulse until combined and butter is about pea sized. Then, while running, add tablespoons of water from your ice water one at a time until a dough forms.
On a floured surface, roll your dough into a ball, wrap in plastic wrap and put back in fridge for at least 30 minutes.
Pre-heat oven to 400 degrees and place rack in center.
Meanwhile, heat a large, deep saute pan with butter. Add garlic and onion (if using whole onion not flakes, if using flakes, wait) with carrots and peas and mushrooms.
Stir for about 2 minutes until onion is translucent or when garlic begins to brown. Add onion flakes (if using)
Add flour and mix well until flour begins to brown. Then add turkey stock and milk, whisking as you add until it begins to thicken.
Once all combined, add in turkey and mix well. Season with salt and pepper as needed. Your flavor here will depend on the flavor/richness of your stock. Optional additions: 1/2 - 1 teaspoon rubbed sage, 1/2-1 teaspoon fresh minced or dried thyme.
In a 1 1/2 quart casserole dish or pie pan (about a 10 in X 2 in pan) add your turkey mixture and set aside.
Remove dough from fridge. Roll out dough until 1/4 - 1/2 inch thick round and gently place over the top of your dish. Trim excess dough from the edges just below the lip of the pan edge and pinch edges around. With excess dough add addition cut outs, if desired, and with a sharp knife cut cut 4 small vent holes in the top of the pie.
With a pastry brush, brush the top of the pie with egg wash.
Bake for 25-30 minutes or until crust is golden.
Cool for 5 minutes and then enjoy!