In a saucepan, combine carrots and celery. Add water to cover and boil for 15 minutes. Remove from heat, 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 chicken broth and milk. Simmer over medium-low heat until thick. Remove from heat and add in green peas.
Place the turkey mixture in bottom pie crust. Pour hot liquid mixture over. Cut edge off top crust and cover and seal edges. Make several small slits in the top to allow steam to escape.
Bake in the preheated oven for 30 to 35 minutes, or until pastry is golden brown and filling is bubbly. Cool for 10 minutes before serving.