In a large mixing bowl, stir together flour and salt. Cut in butter with a pastry blender until mixture is crumbly.
In a 1 or 2-cup measure, beat egg yolk lightly with a fork, adding just enough milk to make 2/3 cup. Stir milk and egg yolk mixture into flour mixture, blending with a fork just until mixture holds together and comes away from side of bowl.
Dived dough into 2 portions. Roll half of the dough out to line a 10 1/2- x 15 1/2- x 1-inch baking pan (jelly roll pan). Place dough in the pan, pressing lightly into bottom and up sides to form the bottom crust.
Sprinkle crushed corn flakes over the bottom crust.
In a large bowl combine apple slices with sugar, ground ginger, and ground cinnamon; stir to blend well. Arrange apple mixture over bottom crust.
Roll out remaining dough and place over top of apples. Pinch edges of dough together to seal. Brush top crust with lightly beaten egg white.
Bake at 400° for 50 to 60 minutes, or until golden brown. Comvine confectioners' sugar and vanilla; stir in enough water to make frosting. Let pastry cool slightly then spread with frosting while still warm. Cut into squares.
Serves 16 to 20
Calories per serving (based on 20 servings): 260