For pastry, in a large bowl combine flour, 2 Tbsp. granulated sugar, and salt. Using a pastry blender, cut in shortening and butter until pieces are pea size.

In a small bowl whisk together egg yolks and milk. Gradually stir egg yolk mixture into flour mixture, tossing with a fork to moisten. Sprinkle the water over mixture, gently tossing until mixture is moistened. Using your fingers, gently knead pastry just until a ball forms. Divide pastry into 2 portions, making one portion slightly larger than the other. Wrap and chill 30 minutes.

Meanwhile, for filling, in an extra-large bowl combine apples, 1 cup granulated sugar, cornflakes, and apple pie spice.

Preheat oven to 350°F. On a lightly floured surface, use your hands to pat the larger portion of pastry into bottom of a 15x10-inch baking pan. Spoon filling evenly into pastry-lined pan.

Roll remaining pastry between 2 pieces of waxed paper to a 15x10-inch rectangle. Carefully peel off top sheet of waxed paper. Invert pastry over apple layer. Carefully peel off waxed paper. Press edges of top and bottom pastry together using wet fingers. Cut a few slits in top pastry; brush lightly with egg white. If you like, sprinkle lightly with coarse sugar.

Bake until pastry is golden, fruit is tender, and filling is bubbly, 45 to 50 minutes. Cool completely in pan on a wire rack. Drizzle with Powdered Sugar Icing. Let stand until icing is set. Cut into bars.

In a small bowl combine powdered sugar, vanilla, and milk. Stir in additional milk, 1 tsp. at a time, until icing reaches drizzling consistency.