Preheat your oven to 375°F (190°C).
In a mixing bowl, combine the flour and vegan butter. Use a fork or pastry cutter to mix until the mixture resembles coarse crumbs.
Gradually add ice water, one tablespoon at a time, until the dough comes together. Divide the dough in half, shape into discs, and refrigerate for at least 30 minutes.
In another bowl, mix the blackberries, sugar, cornstarch, lemon juice, and vanilla extract. Set aside.
Roll out one disc of dough on a floured surface and fit it into a pie dish. Pour the blackberry mixture into the crust.
Roll out the second disc of dough and place it over the filling. Trim and crimp the edges. Cut a few 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 bubbling. Let cool before serving.