In a mixing bowl, combine flour and salt. Cut in butter until mixture resembles coarse crumbs.

Stir in ice water, a tablespoon at a time, until mixture forms a ball. Divide dough in half, shape into discs, wrap in plastic, and refrigerate for at least 30 minutes.

In a large bowl, combine blueberries, blackberries, sugar, cornstarch, lemon juice, vanilla extract, and cinnamon. Toss gently to coat the berries.

Preheat the oven to 375°F (190°C). Roll out one disc of dough to fit the pie dish. Place in the dish and fill with the berry mixture.

Roll out the second disc of dough and place over the filling. Seal and cut slits for steam to escape. Bake for 45 minutes or until crust is golden brown and filling is bubbly.

Allow the pie to cool for at least 15 minutes before slicing. Serve warm or at room temperature.