Preheat the oven to 400°F (200°C)
Melt 1/3 cup butter in a large skillet over medium heat
Add 1/3 cup chopped onion and cook until soft
Stir in 1/3 cup all-purpose flour
Cook for 1 minute
Gradually whisk in 1 3/4 cups chicken broth and 2/3 cup milk
Cook until thickened
Add 2 cups cooked turkey, 1 cup mixed vegetables, 1/2 teaspoon salt, and 1/4 teaspoon black pepper
Stir to combine
Pour the filling into a pie dish or baking dish
Cover with one pie crust or puff pastry sheet
Cut a few slits in the top
Bake for 30 to 35 minutes until golden brown
Let cool for 10 minutes before serving