In a mixing bowl, combine flour and butter until it resembles coarse crumbs. Add ice water and mix until dough forms. Divide dough in half, wrap in plastic, and refrigerate for 30 minutes.
Roll out one half of the dough and fit it into a pie dish. In another bowl, mix blackberries, sugar, cornstarch, and lemon juice. Pour into the pie crust.
Roll out the second half of the dough and place it over the filling. Trim and crimp the edges. Cut slits in the top crust to allow steam to escape.
Bake for 45 minutes or until the crust is golden brown and the filling is bubbly. Let cool before serving.