Prepare the Crust: In a large bowl, whisk together the flour and salt. Add the cold, cubed butter and use a pastry blender or your fingers to cut the butter into the flour until the mixture resembles coarse crumbs. Gradually add the ice water, one tablespoon at a time, mixing until the dough just comes together. Be careful not to overmix. Divide the dough in half, flatten each half into a disc, wrap in plastic wrap, and refrigerate for at least 30 minutes.

Roll Out the Dough: On a lightly floured surface, roll out one disc of dough into a 12-inch circle. Carefully transfer the dough to a 9-inch pie plate. Trim the edges and crimp the crust using a fork or your fingers. Place the pie plate with the crust in the refrigerator while you prepare the filling. Roll out the second disc of dough and cut into strips for a lattice top, or use cookie cutters to create decorative shapes.

Make the Blackberry Filling: In a large bowl, gently combine the fresh blackberries, granulated sugar, flour, lemon juice, and cinnamon. Mix until the blackberries are evenly coated.

Assemble the Pie: Pour the blackberry filling into the prepared pie crust. Dot the top of the filling with the small pieces of butter. Arrange the dough strips over the filling in a lattice pattern, or place your decorative shapes on top. Trim any excess dough and crimp the edges to seal.

Bake the Pie: Preheat your oven to 375°F (190°C). Place the Classic Blackberry Pie on a baking sheet and bake for 45-55 minutes, or until the crust is golden brown and the filling is bubbling. If the crust starts to brown too quickly, you can cover the edges with foil or use a pie shield.

Cool and Serve: Remove the pie from the oven and let it cool completely on a wire rack before slicing and serving.