In a large saucepan cook leek, mushrooms, celery, and sweet pepper in hot butter over medium heat for 4 to 5 minutes or until vegetables are tender. Stir in the flour, poultry seasoning, salt, and pepper. Add broth and half-and-half all at once. Cook and stir until thickened and bubbly. Stir in chicken and peas. Pour into a 2-quart rectangular baking dish.
Place pastry over chicken mixture in dish. Turn edges of pastry under; flute to edges of dish. Brush pastry with some of the egg. If desired, place cut-out pastry shapes on top of pastry. Brush again with egg.
Bake, uncovered, in a 400 degree F oven for 30 to 35 minutes or until crust is golden brown. Let stand for 20 minutes before serving. Makes 6 servings.
In a medium bowl stir together 1-1/4 cups all-purpose flour and 1/4 teaspoon salt. Using a pastry blender, cut in 1/3 cup shortening until dough pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with a fork. Push moistened dough to side of bowl. Sprinkle an additional 3 to 4 tablespoons cold water over remaining flour mixture, 1 tablespoon at a time, tossing with a fork until all dough is moistened. Form into a ball. On a lightly floured surface, roll dough into a 13x9-inch rectangle. Using a sharp knife, cut slits in pastry to allow steam to escape, or, if desired, use a small cookie cutter to cut shapes from pastry.