Preheat oven to 350°. In a medium saucepan, saute celery and onion in butter until tender. Add 2 cups water, chicken, vegetables, noodles, bouillon and pepper. Cook, uncovered, over medium heat for 5 minutes or just until noodles are tender, stirring occasionally. Combine cornstarch and remaining water; add to saucepan. Bring to a boil. Reduce heat; cook and stir for 2 minutes or until thickened and bubbly.
Pour into an ungreased 10-in. pie plate. Roll dough to a 1/8-in.-thick circle. Place over filling. Trim and flute edge. Cut slits in top.
Bake until lightly browned and filling is bubbly, 45-55 minutes. Let stand for 5 minutes before serving.
Combine 1-1/4 cups all-purpose flour and 1/4 tsp. salt; cut in 1/2 cup cold butter until crumbly. Gradually add 3-5 Tbsp. ice water, tossing with a fork until dough holds together when pressed. Shape into a disk; wrap and refrigerate 1 hour.