In a medium bowl combine flour and salt. Add cold cubed butter and shortening.
Mix the butter, shortening, flour and salt together with a pastry cutter until it resembles coarse crumbs.
Add ice cold water to the dough a little at a time just until the dough comes together.
Separate the dough into two equal portions, wrap in plastic wrap and refrigerate for about an hour and up to 3 days.
Remove one dough ball from the refrigerator and roll it out into a 13-inch circle and transfer to a 9-inch pie dish. Place the crust back in the fridge until ready.
In a medium bowl mix blackberries, lemon zest, lemon juice, cinnamon, salt, sugar, and cornstarch.
Transfer the pie filling to the pie dish, and place in the refrigerator.
Remove the other ball of dough from the refrigerator and roll it out into a 12-inch circle. Use a knife or pastry wheel (or pizza cutter!) to cut the circle into 10-12 equal strips.
Retrieve the bottom crust from the refrigerator and trim excess dough from the edges using scissors. You can leave about 1 inch of excess to create a thick pie crust, or trim more if you prefer a thinner crust.
Arrange the pie crust strips on top of the pie in a lattice pattern. Pinch the edges to seal. For a detailed tutorial, check out my lattice pie crust post!
Mix egg and water together to create an egg wash. Brush the lattice top with the mixture.
Bake the pie for 20 minutes at 425°F/220°C, then reduce the heat to 375°F/190°C and continue baking for 30 minutes.
Allow the pie to cool down for at least two hours before serving as is, or with a scoop of vanilla ice cream.