Preheat your oven to 400°. Take out pie crusts from fridge.
In a medium saucepan over medium heat, melt the butter. Add the onion and cook for 2 minutes.
Add the flour, salt, pepper, & thyme. Stir until blended with the melted butter.
Slowly add the chicken broth and milk. Whisk the mixture until smooth. Keep cooking and stirring until it thickens. (This will take a few minutes)
Add shredded chicken and frozen vegetables. Stir to combine.
Line a 9 inch pie plate with one pie crust. Pour the filling in and top with the second crust.
Pinch the edges of the pie crust together to seal and cut an X on the top for venting.
Place pie plate on top of a small cookie sheet and bake for 30 minutes or until the crust looks golden brown.
Let cool off for 10 minutes before serving