Combine flour and salt, cut in shortening. Beat egg yolk in measuring cup and add enough milk to make 2/3 cup liquid. Mix well and add to the flour mixture. On floured surface roll half the dough out. Put in a 15 1/2 x 10 1/2 inch pan. Sprinkle the bottom crust with corn flakes. Top with apples. Combine sugar and cinnamon and sprinkle on top. Roll out the remainder of dough. Place on top. Beat egg white until frothy. Brush on crust. Bake at 350ºF. for 1 hour. While still hot, drizzle with a powdered sugar frosting.