Preheat oven to 400°F (200°C).

In a large skillet, melt butter over medium heat. Add onion and celery and cook until softened, about 5 minutes.

Sprinkle flour over the vegetables and stir for 1 minute.

Gradually whisk in chicken broth and milk until smooth. Bring to a simmer, stirring constantly, until thickened.

Stir in cooked chicken, frozen peas, carrots, and corn. Season with salt and pepper.

Line 6 individual oven-safe dishes or ramekins with one pie crust sheet each, pressing to fit the bottom and sides. You may need to cut the crusts to fit.

Divide the chicken filling evenly among the prepared dishes.

Top each dish with a second pie crust sheet. Crimp the edges to seal and cut slits in the top to allow steam to escape.

Place the dishes on a baking sheet and bake for 30-35 minutes, or until crust is golden brown and filling is bubbly.

Let cool slightly before serving. These can also be cooled completely, wrapped tightly, and frozen for later. To reheat, bake from frozen at 375°F (190°C) for about 45-55 minutes, or until heated through.