Preheat oven to 375 degrees.
Remove pie crust from refrigerator and allow to come to room temperature.
Dice your cooked chicken and onion.
Heat unsalted butter in a frying pan over medium heat. Add diced onions and sauté for 3-4 minutes until begin to turn translucent. Next add minced garlic and cook for 1 more minute.
Add cream of chicken, chicken and salt and pepper. Stir to combine.
Next add milk, frozen vegetables. Combine all ingredients and allow to warm for a few minutes on low heat.
When oven is ready, roll out pie crust and place the 1st crust in the bottom of your pie dish. Using a fork poke a few holes in the crust.
Scoop your pot pie "filling" into the pie dish and top with 2nd crust.
Fold the two crust edges together so the filling will not be able to escape.
Using a knife, cut 3-4 slits into the pie to create "vents". Whisk your egg and lightly brush the egg wash on top of the crust.
Bake your chicken pot pie in the oven for 30 minutes until crust is completely cooked.
Remove from the oven. Allow to cool for 5 minutes, serve & enjoy!