Prepare Pastry, set aside.
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 the mixture 1 Tbsp at a time, gently toss 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 (I like to wait and do this once it on the pie - makes moving it a lot easier).