Preheat the oven to 355°F
To make the pastry, cream the butter and sugar together using a wooden spoon or a food mixer. Add the eggs and beat for several minutes. Reduce speed and mix in the flour. Turn out onto a floured board and roll into a round shape, wrap with cling film and chill in the fridge for at least 1 hour, this will give it a crumblier texture once baked.
To make the pie, roll out 2/3 of the pastry so that it’s about 1/8 inch (3mm) thick, and line a 9inch flat plate. Trim the edges with a knife, pop into a fridge to chill again while you prepare the blackberries.
Wash the blackberries and remove the pastry plate from the fridge. Evenly place the blackberries on top of the pastry lined dish and sprinkle with the sugar, cinnamon and lemon zest.
To create the lid for the pie, roll out the remaining pastry until it’s 1/8 inch (3mm) thick and cut it into 8 strips. Arrange and weave the pastry strips in a lattice pattern on top of the pie and crimp it all the way around with your fingers and thumb.
Brush the pie all over with the egg wash and sprinkle with caster sugar. Pop it in the fridge to chill for another 30 minutes.
Once chilled, bake in the preheated oven until the blackberries are tender, approx. 45 minutes to 1 hour. Then allow to cool on a wire rack.
Serve warm with whipped cream or vanilla ice cream.