For the pastry topper, in a medium mixing bowl stir together 1-1/4 cups all-purpose flour and 1/4 teaspoon salt. Using a pastry blender, cut in shortening until pieces are the size of small peas. Sprinkle 1 tablespoon cold water over part of the mixture; gently toss with fork. Push moistened dough to side of bowl. Repeat with 3 to 4 tablespoons cold water, using 1 tablespoon at a time, until all dough is moistened. Form into a ball.
On a lightly floured surface, roll Pastry Topper into a rectangle 1/8 inch thick. Trim to a rectangle 1 inch larger than a 2-quart rectangular baking dish. Using a sharp knife or small cookie cutter, cut some shapes out of center of pastry. Set aside.
In a large saucepan melt margarine or butter over medium heat. Add the leeks or onion, mushrooms, celery, and red sweet pepper; cook for 4 to 5 minutes or until tender. Stir in the 1/3 cup flour, poultry seasoning, 1/2 teaspoon salt, and black pepper. Add the broth and half-and-half, light cream, or milk all at once. Cook and stir until thickened and bubbly. Stir in the cooked chicken and peas. Pour into a baking dish.
Place pastry over the hot chicken mixture in dish; turn edges of pastry under and flute on top of pastry. Brush with the egg. Place reserved pastry shapes on top of pastry. Brush again with egg.
Bake in a 400 degree F oven for 30 to 35 minutes or until the crust is golden brown. Cool about 20 minutes before serving. Makes 6 servings.