Heat oven to 350°F. In large bowl, mix flour, 2 tablespoons sugar, the salt and lemon peel. With pastry blender or fork, cut in butter and shortening until mixture resembles coarse crumbs. Stir in egg yolks and 1/2 cup of the milk. With fork, stir until mixture leaves sides of bowl and forms a ball, adding milk 1 tablespoon at a time as necessary. Form dough into 2 balls.
On lightly floured surface, roll out 1 dough ball to 17x12-inch rectangle. Carefully place in ungreased 15x10x1-inch pan; press in pan and up sides. (Dough may not come completely to top of pan.) Sprinkle dough evenly with crushed cereal. Arrange apples evenly over cereal. Sprinkle with 3/4 cup sugar and crystallized ginger; drizzle with lemon juice.
Roll out remaining dough ball to 15x10-inch rectangle. Carefully place over apples; press to edges. Brush top with egg whites; sprinkle with 3 tablespoons sugar. Make small slits in top of dough.
Bake 55 to 65 minutes or until golden brown and apples are tender. Cool 1 hour. Serve warm or cool.