2. In a Dutch oven (large pan), over medium heat, cook onions and celery in butter until soft and translucent(if using fresh vegetables sauté with onions and celery). Add 4 cups of water, chicken broth, chicken (if chicken is frozen let cook 3-5 min.in water/broth mixture, scoop out, cut up and return to dutch oven before adding next ingredients), potatoes and frozen vegetables and boil for 15 minutes. Remove from heat.
3. In a bowl or cup stir together 1 cup cold water, flour, salt, pepper, and celery seed. Crush rosemary leaves between your palms and add to water/flour mixture. Return chicken mixture to heat, add water/flour mixture stir, Simmer over medium-low heat until thick. Remove from heat and set aside. (I like lots of thick sauce, I add a second cup of water and ¼ to ½ cup more flour to water/flour mixture when it seems dry)
4. Place the chicken mixture in bottom pie crust. Cover with top crust, seal edges, and cut away excess dough. Make several small slits in the top to allow steam to escape.
5. 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. (If made ahead cook for 35 to 45 minutes or until pastry is golden brown and filling is bubbly)