- Preheat your oven to 425°F (220°C). 
- In a large bowl, combine blackberries, sugar, flour, lemon zest, lemon juice, cinnamon, and salt. 
- Toss gently until the berries are well-coated. 
- Roll out one pie crust and fit it into a 9-inch pie plate, leaving an overhang around the edges. 
- Pour the berry mixture into the pie crust. 
- Dot the top with small pieces of butter. 
- Roll out the second pie crust and place it over the berries. 
- Trim the excess dough and crimp the edges to seal. 
- Cut a few slits in the top crust to allow steam to escape. 
- Brush the crust with beaten egg to give it a golden finish. 
- Place the pie on a baking sheet to catch any drips and bake for 45-50 minutes, or until the crust is golden and the filling is bubbling. 
- Allow the pie to cool on a wire rack for at least 2 hours before serving.