Heat your oven to 425 degrees Fahrenheit. Dice your cooked chicken into small chunks.
Chop the onion into tiny pieces. Measure out all your other ingredients now. This saves you time while cooking later.
Melt butter in your skillet over medium heat. Add the diced onions to the pan.
Cook them until they become soft and clear. Sprinkle flour over the butter and onions. Stir constantly for one full minute only.
Pour in chicken broth very slowly while stirring. Add the milk and keep stirring everything together.
The mixture will get thick like gravy. This usually takes about five minutes total. Season it with salt and black pepper.
Add your chicken pieces to the sauce. Toss in all the frozen vegetables too.
Stir until everything is mixed well together. Let it bubble gently for three minutes. Remove the skillet from the heat completely.
Line your pie dish with one crust. Pour the chicken filling into the crust.
Cover it with the second pie crust. Press the edges together to seal tightly.
Cut four small slits on the top. This lets steam escape while it bakes.
Put the pie in your hot oven. Bake for 30 to 35 minutes exactly.
The top should be golden and gorgeous. Let it rest for 10 minutes minimum. Then slice and serve to your family.