How to Make It
In a large bowl, combine the flour and salt. Using a pastry blender or 2 knives, cut the shortening and butter into the flour until it resembles coarse meal. Refrigerate the mixture for a few minutes if the butter becomes too soft to work with.
Dribble the ice water over the flour mixture and, using a wooden spoon, stir just until the dough can be gathered into a ball. Divide the dough in half and pat each piece into a 6-inch disk. Wrap each disk in plastic wrap and refrigerate until firm, at least 2 hours or overnight, before using.
Preheat the oven to 400°. Roll each disk of dough into a 12-inch round. Line a 9-inch pie pan with 1 round of the dough and refrigerate both it and the second round until ready to fill.
In a large bowl, toss together the apples, cranberries, orange zest, sugar, flour and slat; transfer to the pie shell. Brush the edges of the pie shell with the egg wash and cover with the second dough round, lightly pressing the edges together. Trim any overhanging dough under and crimp to seal. Brush the top crust with the egg wash, avoiding the decorative rim as it tends to brown more quickly. Make 4 small slashes in the top crust for venting.
Set the pie on the middle shelf of the oven and place a baking sheet on the lower shelf to catch any drips. Bake the pie for about 1 hour and 10 minutes, or until the crust is light golden and the juices bubble. Cover the pie loosely with foil during the last 15 minutes to prevent excessive browning. Allow the pie to cool on a rack for 20 minutes; serve while still warm.