Make sure to have your pie crust made, and chilling.
Combine the potatoes, onion, carrot, and ½ teaspoon salt in an Instant Pot or pressure cooker. Add 3 tablespoons water. Cook on high pressure for 2 minutes and manually release the pressure when time is up. Alternatively steam or microwave the vegetables, covered, until just tender but not overly soft. They will continue to cook in the pie.
Heat oven to 400ºF. In a saucepan over medium heat melt the butter. Add the flour and cornstarch and whisk until combined and smooth. Whisk in the chicken broth, whisking vigorously until smooth and incorporated. Add the Worcestershire, Better Than Bouillon, thyme, parsley, black pepper and ½ teaspoon salt. Cook, stirring constantly until mixture is boiling. Boil, stirring, for 1 minute and remove from heat.
In a large mixing bowl (or the insert of the Instant Pot) combine the cooked vegetables, gravy, turkey, and peas. Taste mixture and season with salt to taste.
Transfer filling to a 9-inch deep dish pie plate. You can also use a 9-by-9-inch baking dish or pan (it should be a 2½-to-3-quart capacity).
Roll out pastry crust, to a 12-inch circle, on a lightly floured surface and top the pie. Trim the edges to about an inch overhang and fold under. Crimp crust edges as desired.
Whisk together the egg and 1 tablespoon water. Brush some egg wash over the crust. Make 4 or 5 vent holes in the top crust with a knife.
Bake, on a foil-lined baking sheet to catch the drips, until crust is golden and center is bubbling and hot, 35 to 40 minutes. Cover crust with foil or a pie shield if the crust gets dark brown. Let cool 10 to 15 minutes before serving.
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Notes
Pot pie can be frozen, uncooked. Prepare up until baking and wrap in plastic wrap, then aluminum foil. Freeze for up to 3 months.To cook from frozen, do not thaw. Bake as directed in the recipe, increasing time to 50 to 60 minutes baking time. • You can make a gluten-free turkey pot pie by using gluten-free all-purpose flour and a gluten-free pastry crust.• Make a chicken pot pie by swapping the turkey for cooked chicken and using chicken broth.• Make a beef pot pie by swapping the turkey for cooked, diced roast beef. Use thyme, not sage, and beef broth and bouillon rather than the poultry flavors.