Preheat your oven to 400°F. Gotta get that heat ready while you work on the filling.
Melt the butter in a skillet over medium heat. Toss in your diced onion and cook until you see them turn translucent and soft.
Stir in the flour, poultry seasoning, and thyme leaves. Cook this mix for 1-2 minutes. You want it lightly browned but careful not to burn it.
Gradually pour in chicken broth and milk or cream, stirring nonstop. Keep at it till it thickens, looking like a creamy dream.
Add your cooked potato and thawed frozen veggies now. Mix everything well so all the flavors marry up nice.
Pour this yummy filling into one half of the pie crust. Sprinkle chopped turkey evenly over the top.
Cover with second crust, pinch edges to seal, then brush with beaten egg. Slide your pie into the oven and bake for about 25 to 30 minutes till golden brown. That crust gonna be crispy and inviting.
Notes
Refrigerate leftovers for up to 3 days, or freeze for up to 2 months. Use chicken as a substitute for turkey if desired.