Preheat oven to 375 degrees F. In a very large bowl combine granulated sugar, flour, nutmeg, and ginger. Add pear slices and cranberries; toss gently to coat. Transfer to an ungreased 2-quart round baking dish or casserole.
On a lightly floured surface, flatten Pastry dough. Using a rolling pin, roll dough from center to edge into a circle that is about 1 inch wider than the top of the baking dish or casserole. Using cookie cutters, cut a few small shapes from center of the pastry. Set shapes aside. Transfer the dough circle to the top of the fruit mixture. Trim edge as needed to fit the baking dish or casserole; if desired, crimp edge. Brush top of pastry and dough cutouts with milk. Place dough cutouts on the pastry, leaving openings for air to vent.
Place baking dish or casserole on a foil-lined baking sheet. If desired, sprinkle with demerara sugar. Bake, uncovered, for 55 to 60 minutes or until pear mixture is bubbly. Cool pie on a wire rack about 30 minutes and serve warm. (Or cool completely before serving.)
In a medium bowl stir together cake flour, whole wheat flour, and salt. Using a pastry blender, cut in chilled butter until pieces are pea-size. Sprinkle 1 tablespoon cold water over part of the flour mixture; gently toss with a fork. Push moistened dough to the side of the bowl. Repeat moistening flour mixture, using 1 tablespoon cold water at a time, until all of the flour mixture is moistened (3 to 4 tablespoons cold water total). Shape dough into a ball.