Prepare your bottom pie crust as directed on package.
On stove top, heat butter and onion until tender. Stir in flour, salt and pepper. Gradually stir in chicken broth and milk. Stir constantly until thickened.
Add in chicken and veggies. Remove from heat and spoon mixture into bottom crust.
Cut slits (or carve design) into your top crust and lay on top of your pot pie.