Bring pie crusts to room temperature, about 15 minutes
Heat oven to 425°F.
In a saucepan, combine carrots, peas, and celery. Add water to cover and boil for 15 minutes. Remove from heat and drain and set aside.
In the saucepan over medium heat, cook onions in butter until soft and translucent. Stir in flour, salt, pepper, and celery seed. Slowly stir in chick broth and milk. Simmer over medium-low heat until thick, stirring frequently. Remove from heat, and set aside.
Add rotisserie to drained vegetable mix
Place 1 pie crust in the bottom of a pie baking dish.
Place the chicken and vegetable mixture in the bottom pie crust. Pour hot liquid mixture over. Cover with top crust. Seal edges, and cut away excess dough. Make several small slits in the top to allow steam to escape.
Bake for 30-35 minutes or until pastry is golden brown and filling is bubbly. Cool for 10 minutes.