1. 1. In a food processor, pulse the flour and salt. Add the chilled butter and pulse until the mixture resembles coarse crumbs. Gradually add the ice water and pulse just until the dough starts to come together.

2. 2. Divide the dough in half, shape each half into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour.

3. 3. In a large bowl, combine the blackberries, granulated sugar, cornstarch, and lemon juice. Toss gently to coat.

4. 4. Roll out one disk of dough to fit a 9-inch pie plate. Transfer the dough to the pie plate and trim the edges, leaving a 1-inch overhang.

5. 5. Add the blackberry filling to the pie crust. Roll out the remaining dough and cut into strips for a lattice top. Arrange the strips in a lattice pattern over the filling.

6. 6. Crimp the edges of the pie crust and brush the top with the beaten egg. Sprinkle with the coarse sugar.

7. 7. Bake at 400°F for 25 minutes, then reduce the temperature to 350°F and bake for an additional 30-35 minutes, or until the crust is golden brown and the filling is bubbling.

8. 8. Allow the pie to cool completely before slicing and serving.