In a mixing bowl, combine flour and salt. Add cold butter and mix until the mixture resembles coarse crumbs.

Gradually add ice water, mixing until the dough comes together. Divide into two discs, wrap in plastic, and refrigerate for at least 1 hour.

In a large bowl, combine blackberries, sugar, cornstarch, lemon juice, and vanilla extract. Gently toss to coat the berries.

Preheat the oven to 425°F (220°C). Roll out one disc of dough on a floured surface to fit the pie dish.

Place the rolled dough in the pie dish and fill with the blackberry mixture. Dot with butter.

Roll out the second disc of dough and place it over the filling. Cut slits for steam to escape and crimp the edges to seal.

Bake in the preheated oven for 45-50 minutes, or until the crust is golden brown and the filling is bubbly.

Allow to cool before serving to let the filling set.