In a large mixing bowl stir together the flour and the salt. Cut in shortening till the mixture resembles coarse crumbs. Lightly beat egg yolk in a glass measuring cup. Add milk to make 2/3 cup liquid total; mix well. Divide dough in half.
On a floured surface, roll half the dough to an 18 x 12 inch rectangle; fit into and up sides of a 15 x 10 x 1 inch baking pan.
Sprinkle with corn flake cereal; top with apples. Combine sugar and cinnamon; sprinkle over apples.
Roll remaining dough to a 16 x 12 inch rectangle; place over apples. Seal edges; cut slits in the top for steam to escape. Bake at 375 degrees F (190 degrees C) for about 50 minutes or until golden brown. Cool on a wire rack.