Chill the prepared vegan double-crust pastry. Roll one dough portion into a circle about 12 inches wide and 1/8 inch thick. Set it into a 9-inch pie dish and refrigerate while preparing the filling.

Gently rinse fresh blackberries as needed and dry them thoroughly. Keep frozen berries frozen until mixing.

Preheat the oven to 425°F (220°C) with a rack in the lower third. If using a metal pie plate, prepare a rimmed baking sheet. Avoid setting a cold glass or ceramic pie dish on an already preheated baking sheet.

Rub the finely grated lemon zest into the coconut sugar until intensely fragrant. Whisk in the cornstarch, cinnamon and salt until evenly dispersed.

Toss the blackberries gently with the lemon-sugar mixture, fresh lemon juice and blackberry liqueur, brandy or blackberry juice. Spoon the coated berries and any juices into the chilled pastry.

Roll the second dough portion to approximately 1/8 inch thick. Cut strips approximately 3/4 inch wide and weave a lattice over the filling. Trim, tuck and crimp the edges. If using a full top crust, cut several steam vents instead.

Brush the pastry lightly with plant milk if desired, then refrigerate the assembled pie for 15–20 minutes.

Bake at 425°F (220°C) for 20 minutes on the lower rack.

Reduce oven heat to 375°F (190°C) and continue baking about 40–55 minutes, until the pastry is golden and the thick blackberry juices actively bubble in the center of the lattice. Allow about 10–15 additional minutes for frozen berries, if needed. Shield the edges loosely with foil if browning too quickly.

Place the baked pie on a wire rack and let cool completely for at least 3–4 hours before slicing, allowing the filling to thicken and settle.