Start by making the pastry. Place the plain flour and salt in a large bowl and whisk to mix or place them in a food processor and pulse until combined.
Add the cold diced vegan block butter and rub it in using your fingers or blend with the food processor until the mixture resembles fine breadcrumbs and no lumps of fat remain.
Add the cold vodka (if using) and mix to combine. Gradually add enough cold water to bring the pastry together into a ball. Shape the pastry into a disc (don't knead it), wrap and refrigerate for about an hour until firm enough to roll out.
Once the pastry has chilled, roll it out thinly on a floured surface until it is large enough to line a 23cm/9 inch round pie dish.
Gently transfer the pastry to the dish and press it right into the corners and over the rim. Trim off the excess pastry and crimp the edge.
Place the pastry base in the freezer for twenty minutes while you preheat the oven to 180°C/160°C fan/350°F/gas mark 4.
Line the pastry case with baking parchment or tin foil, pressing it right into the corners, then fill with baking beans or dried rice, making sure that the sides are propped up.
Bake for 20 minutes then remove the tin foil and baking beans and return the tart shell to the oven for a further 10 minutes until very pale golden. Remove from the oven and set aside.
To make the filling, place the cornstarch in a bowl and gradually whisk in the evaporated coconut milk, making sure that there are no lumps.
In a separate bowl, whisk together the cocoa powder and melted butter until smooth.
Whisk in the sugar, vanilla, espresso powder, evaporated milk mixture and a pinch of salt until the mixture is completely smooth.
Pour the mixture into the pie shell and bake for about 45-50 minutes until the filling is set but still jiggles slightly if you shake the dish.
Switch off the oven and crack open the door. Leave the pie to cool in the oven for 30 minutes then allow to cool completely at room temperature before refrigerating.