Add flour, salt, sugar, and cinnamon to a food processor. Add butter and shortening and process until the mixture resembles coarse crumbs.
Add the water and pulsate to combine. The dough can also be made in a large bowl using a pastry blender or your fingers.
Shape the dough into a ball and divide it into two pieces. Wrap each piece in plastic wrap. Refrigerate for 3 hours or overnight.
When ready to use, place waxed paper on a flat surface and lightly dust it with flour.
Roll one dough ball out to fit a 9-inch pie plate.
Transfer the crust to the pie plate and press evenly into the bottom and sides of the pie dish. Refrigerate it while you work on other things.
Use my recipe for homemade Strawberry Pie Filling, or opt for the store-bought canned version. If making homemade filling, cool it and chill it before using it in the pie.
Preheat oven to 400 degrees F.
Add the strawberry filling to the pie crust and level the top with a spatula. Crimp the edges.
Roll the other dough ball, cut it into strips, and create a lattice pattern for the top of the pie. Trim the edges.
Beat the egg with the water, brush the pie top with the mixture, and sprinkle a bit of sugar on top.
Bake the pie for 20 minutes, then reduce the temperature to 350°F and continue baking for 30-40 minutes. If the edges are getting too brown, tent them with foil.
Cool the pie on a wire rack before transferring it to the refrigerator to chill for 2-3 hours. Slice and serve.
