Start by making the pastry. Place the plain flour, icing sugar and salt in a food processor and pulse until combined.
Add the cold diced vegan block butter or coconut oil (or a mixture of both) and blend until the mixture resembles fine breadcrumbs and no lumps of fat remain.
Add the tablespoon of cold vodka (or water) and pulse again; drizzle in a little cold water as needed to bring the pastry together into a ball.
Cover the pastry and pop it in the fridge for half an hour until it has firmed up. If you are using coconut oil the pastry will firm up very quickly and it will be unworkable if it gets too cold so keep a close eye on it.
Once the pastry has chilled, roll it out on a floured surface until it is large enough to line a 23cm/9 inch round pie dish or a 25cm/10 inch round tart tin.
Gently transfer the pastry to the dish and press it right into the corners. Crimp the edges or trim off the excess pastry as you prefer and prick the base all over with a fork. The coconut oil version is quite delicate but if it cracks then you can just press it back together with your fingers.
Place the pastry base in the freezer for twenty minutes while you preheat the oven to 200°C/400°F/gas mark 6.
When the pastry is nice and cold, line it with tin foil, making sure that you press it right into the corners, then fill it with baking beans or dried rice. Make sure you spread them right into the corners.
Bake for 20 minutes then remove the tin foil and rice/beans and return the tart shell to the oven for 15 minutes or so, until it is golden and crisp. Place the baked shell on a wire rack and turn the oven down to 180°C/350°F/gas mark 4.
Place the pumpkin puree, silken tofu, cornflour (cornstarch), sugar, maple syrup, spices, vanilla and salt in a blender and blitz until totally smooth.
Pour the filling into the case and spread it level. Bake for 35-45 minutes until the filling is set but still has a slight wobble in the middle. If you use a 9 inch pie dish it will take nearer the 45 minute mark to cook through, and if you use a wider, shallower 10 inch tart tin it will take less time to cook.
Once the pie is baked, leave it to cool completely on a wire rack at room temperature then refrigerate it overnight before serving.