In a food processor, combine all-purpose flour, salt, sugar, and optional ground cinnamon. Cut in cold unsalted butter and cold shortening until the mixture resembles coarse crumbs, about 10 seconds. Gradually add cold water, pulsing until the dough just comes together.

Shape the dough into a ball, then divide it into two equal halves. Wrap each half in plastic wrap and refrigerate for at least 3 hours or overnight for best texture.

On a lightly floured surface, roll out one dough ball to about 1/8-inch thickness for your 9-inch pie plate. Carefully transfer the rolled-out dough to the pie plate, pressing it gently into the bottom and up the sides.

Prepare the strawberry pie filling according to your preference and ensure it is cool before adding. Spoon the filling into the prepared crust, making sure it is spread evenly.

Roll out the second dough ball on the floured surface until it matches the size of the pie plate. Cut the rolled dough into strips about 1-inch wide. Create a lattice pattern by arranging the strips over the filling.

In a small bowl, beat an egg with a tablespoon of water to create an egg wash. Using a pastry brush, gently apply the egg wash over the lattice and crust edges.

Preheat your oven to 400°F (200°C). Place the prepared pie in the oven and bake for 20 minutes, then lower the temperature to 350°F (175°C) and bake for an additional 30 to 40 minutes.

Once baked, carefully remove the pie from the oven and allow it to cool on a wire rack. Let the pie chill in the refrigerator for 2 to 3 hours before serving.