In a large mixing bowl combine the flour, the 2 Tbsp. sugar, and salt. Using a pastry blender, cut in the shortening and butter until pieces resemble small peas.
Sprinkle 1 Tbsp. of the ice water over part of the flour mixture; toss with a fork. Push moistened flour mixture to side of bowl. Repeat moistening flour mixture, using 1 Tbsp. of water at a time, until flour mixture is moistened. Gather flour mixture into a ball, kneading gently until it holds together. Divide into 2 uneven balls; one ball should contain two-thirds of the pastry. Cover; set aside.
For Double Cherry Filling
In a large mixing bowl combine frozen cherries, dried cherries, 1 cup granulated sugar, the cornflakes, and lemon peel. Set aside.
Preheat oven to 350 degrees F. Place larger ball of pastry between two pieces of lightly floured waxed paper. Roll to a 17x12-inch rectangle. Remove top piece of waxed paper. Carefully invert pastry into a 15x10x1-inch baking pan. Peel off waxed paper. Press pastry up sides of pan.
Spoon filling evenly over pastry. Roll remaining pastry to a 16x11-inch rectangle between 2 pieces of lightly floured waxed paper. Remove top sheet of waxed paper. Using a 3-inch heart-shape cutter, cut hearts out of pastry; set aside. Invert pastry over filling. In a small bowl whisk together egg white and 1 Tbsp. water. Brush pastry with egg white mixture.
Bake for 45 minutes or until golden brown. Cool completely in pan on wire rack.