Preheat the oven to 375 degrees F (190 degrees C). Grease a 10x15 inch jellyroll pan or cookie sheet.
In a large bowl, stir together the salt and 4 cups flour.
Cut in the shortening until the mixture resembles coarse crumbs. Use a fork to stir in the egg yolks and milk just until dough comes together. On a lightly floured surface, roll out half of the dough to 1/8 inch thickness or until big enough to cover the bottom of the jellyroll pan with a little hanging over the sides.
Arrange the slices of apple to evenly cover the bottom crust. In a small bowl, stir together the 2 tablespoons of flour with the sugar and cinnamon.
Sprinkle the sugar mixture over the apple slices.
Roll out the remaining dough to cover the apple layer and pinch to seal to the bottom crust. Trim off excess crust and brush with egg white.
Bake for 40 to 45 minutes in the preheated oven, until apples are tender and crust is brown. If the crust begins to brown too much before the apples are done, cover with foil and continue baking. Cool before cutting into squares.
