In a large bowl, whisk together the flour, sugar, and salt.
Cut COLD butter into small chunks and add to the dry ingredients.
Add shortening to bowl and using a pastry cutter, cut butter and shortening into the mix.
When most of the butter is incorporated into the flour, add egg and ice water.
Mix together with the dry ingredients.
Using clean hands, knead the dough making sure to incorporate all of the dry mix.
Add more water as needed.
Once dough is smooth and you can shape it into a ball, wrap dough in plastic wrap and place in the refrigerator for 30-45 minutes.
Once chilled, transfer dough to a well floured surface and roll out dough in a 9x13 size rectangle.
Place rolled out crust into the prepared baking dish and trim away excess dough. We just want the bottom of the dish to be covered with crust.
Place in preheated oven and prebake crust for 15-20 minutes then remove from the oven.