Shape each part into flattened round on lightly floured cloth-covered board. Roll one part into rectangle, 15x10 inches, fold into thirds. Place in jelly roll pan; unfold to cover bottom of pan. Sprinkle crushed cereal on pastry.

Mix apples, sugar, cinnamon and allspice; spread over cereal. Roll remaining pastry into rectangle 15x10 inch, fold into thirds. Gently place over apples, unfold.

Beat egg white until soft peaks form; spread over pastry. Bake until crust is golden brown, 55 to 60 minutes.

Mix powdered sugar, vanilla and water until smooth; drizzle over warm crust. Cut into bars, about 3 x 1 1/2 inches.