Let the pie crusts sit at room temperature for 15 minutes after removing them from their packaging. Preheat your oven to 425°F (220°C).

Place one pie crust in an ungreased 9-inch glass pie plate. Press it firmly against the sides and bottom, leaving any excess hanging over the edge.

In a 2-quart saucepan, melt the butter over medium heat. Add the chopped onion and cook for about 2 minutes, stirring frequently, until the onion is tender.

Stir in the flour, salt, and pepper until everything is well combined.

Gradually add the broth and milk, stirring constantly. Continue cooking until the mixture becomes bubbly and thickened.

Add the cooked chicken and mixed vegetables, stirring until everything is evenly combined. Remove from heat.

Spoon the chicken mixture into the prepared pie crust.

Place the second pie crust over the filling. Fold any extra top crust under the edge of the bottom crust, pressing the edges together to seal and create a thick rim.

Flute the edges by placing your thumb and index finger about an inch apart on the outside edge, then use your other thumb to push the pastry outward, forming a scalloped pattern.

Use a small knife to cut several slits or decorative shapes in the top crust to allow steam to escape during baking.

Bake for 15 minutes. Then, cover the edge of the crust with foil to prevent over-browning.

Continue baking for another 15 to 25 minutes, or until the top is golden brown and the filling reaches at least 165°F (74°C). Let the pie stand for 5 minutes before serving.