Heat the Dr Pepper in a small saucepan over medium-high heat. Add the blueberries, brown sugar, cinnamon, and lemon zest. Stir well to dissolve the sugar, and cook, stirring frequently, for 20 minutes, or until the sauce has reduced to a jammy consistency and the berries are soft and tender. Pour 1/4 cup of the jam into a small bowl and set aside.
Return the saucepan to the heat and cook for another ten minutes. Allow the jam to come to room temperature, transfer to a bowl, and refrigerate until ready to use.
In a medium bowl whisk together the flour and salt. Cut the frozen shortening and butter into five millimeter cubes and add them to the bowl. Using a pastry cutter or two forks, work the shortening and butter into the flour until the mixture resembles pea-size crumbles.
Add the ice cubes to 1/2 cup water and give it a good stir. Remove the ice and add the chilled water to the dough one tablespoon at a time while stirring with a rubber spatula. The dough will start to clump together but will not be too sticky. Do not add more water than the recipe calls for! With your hands, squeeze the dough to ensure all the flour is worked into the dough. Transfer the dough to a floured work surface and divide it in half. Shape each half into a ball and flatten each into a 2.5 centimeter thick disc. Wrap each disc in plastic wrap and refrigerate for at least two hours.
Line two baking sheets with parchment paper. Dust a rolling pin and work surface with flour and roll out one disc of dough into a 30 x 23 centimeter rectangle about three millimeters thick. Cut out eight or nine 10 x 8 centimeter rectangles and place them on a baking sheet.
Return to the refrigerator while you repeat this process with the second disc of dough. Keep the pastry in the fridge until you are ready to use it.
Preheat the oven to 350°F (180°C). In a small bowl whisk the egg with the remaining two tablespoons water. Take the first tray of pastry rectangles out of the refrigerator—these will be the bottoms of your hand pies. Brush the edges of each rectangle with some egg wash, then spoon one tablespoon Dr Pepper Blueberry Jam into the centre of each. Remove the second tray of pastry rectangles from the refrigerator and again, brush the edges of each rectangle with egg wash. Place a top on each pie, egg washed side down, and use the tines of a fork to seal the edges. Poke a few slits in the top of each pie—this will allow steam to escape. Now place the pies back in the refrigerator to chill for 20 minutes. Remove the chilled pies from the refrigerator and brush with the remaining egg wash. Bake for 30 minutes, or until they are golden brown, rotating the baking sheet halfway through so the pies bake evenly.
While the pies are baking, make the icing by combining the 1/4 cup reserved jam, icing sugar, and cream in a food processor and blending until smooth.
Transfer the pies to a rack and allow to cool for five minutes before covering them in the purple icing.