One hour prior to making pie, place flour and shortening in the freezer.
Preheat oven to 425 F.
In a medium mixing bowl, mix sugar, cornstarch, cinnamon, salt, and zest together. Set aside. Place grated apple in a towel or paper towel and ring out juice. In a large mixing bowl, combine blueberries, grated apple, and lemon juice. Set aside.
In a large bowl, mix flour and salt together. Cut shortening into flour using a pastry cutter or fork until it's the size of peas. Add one tablespoon ice water at a time to the mixture, gently stirring in between. Once the dough starts to come together as a ball, stop adding water and gently press any straggling flour/dough into the ball. Divide in half and place one half on a lightly floured work surface (place the other in the fridge while you work). With floured hands, form the dough into a disk. Flour rolling pin and begin to roll the dough out from the middle to the edge, rotating the dough 90 degrees between each roll to make sure it doesn't stick. (Add more flour to the surface or rolling pin as needed.) Roll it out to no thicker than 1/4 inch thick. You'll want to take your pie dish and hold it upside down over your dough and make sure that your dough is an inch wider all the way around than the very edge of the dish. Fold the dough in half or kind of roll it over the rolling pin and lay it in the center of the pie dish and lightly press it into the dish.
Add the sugar mixture to the blueberries and mix until coated. Pour berries onto pie crust forming a mound (it will cook down).
Roll out the remaining pie dough as done before and lay on top of the berries. Pinch and tuck the top crust under the bottom crust all along the edges and cut off any excess dough. Flute edges and make a few cuts into the top crust to allow steam to vent.
Place pie plate on a baking sheet to catch any drippings and cover the edges with a pie edge protector or with foil (my crust still gets slightly browned with my metal one). Bake for 15 minutes and then turn down temperature to 375 F and bake for 30 minutes. At this point you can remove the edge protector and can lightly brush the top and edges with the egg (you won't use you all of it) and then sprinkle with sugar and cook 5-10 minutes more until crust is golden.
Let pie rest for at least 1-2 hours before cutting (4 hours is best). Serve à la mode.
Blueberry Pie https://www.garnishandglaze.com/blueberry-pie/