Whisk the salt and flour together.
Shred the cold shortening into the flour, and stir with a fork. This should look like flour coated, pea-sized shortening pieces.
Separate the egg, setting the egg white aside. Place the egg yolk and 1 tsp. vinegar into a 1 cup measure, add water to make ⅖ cup. Whisk together until smooth.
Pour the liquid over the flour/shortening mixture and stir with a fork just until all the flour is moistened and you can form a ball.
Divide pastry into two balls. Roll each ball on wax paper the size of a jelly roll pan. Place one crust in the pan, without the wax paper.
Sprinkle slightly crushed corn flakes over the crust layer in the pan.
Spread the apple mixture over the corn flakes, and cover with the second layer of pastry. Remove the wax paper.
Whip the egg white with a small whisk, and brush over the pastry top.
Bake at 350° for 30 minutes.