For the shortcrust:
1) Combine the flour, sugar and salt in the bowl of a food processor and pulse a few times to combine.
2) Scatter the butter and shortening over the top of the flour mixture and pulse until the mixture resembles breadcrumbs.
3) Add the water a few tbsp at a time and pulse until the dough just comes together. Remove the pastry from the machine and lightly knead on a flat surface until it is smooth.
4) Form the pastry into a disk, wrap in cling film and refrigerate for at least an hour.
For the filling:
1) Preheat the oven to 190C/Gas 5. Combine the peaches, sugars, cinnamon, ginger, nutmeg, peach eau de vie and cornflour or tapioca in a large bowl and mix until well combined.
2) Toss the blackberries with the cassis. Allow to stand for 10 mins, then use a slotted spoon to spoon the berries into the peaches, and toss.
3) Divide the pastry in half and roll each half out on a lightly floured surface to 33cm to 35cm round. Transfer 1 of the rounds into the bottom of a 23cm deep-dish pie plate.
4) Spoon the fruit into the crust using a slotted spoon. Add some of the juices that have accumulated in the bowl. Scatter the butter over the top.
5) Roll up the remaining dough over a rolling pin and unroll on top of the pie. Trim the edges of both layers of pastry to a 2cm overhang. Fold the edges over; press to seal. Crimp the edges.
6) Cut 6 slits in the top crust to allow the steam to escape. Brush the top of the pie with the cream and sprinkle with the demerara sugar.
7) Place the pie on a baking sheet and bake on the bottom rack of the oven for about 1 hr 20 to 30 mins until the crust is golden brown and juices bubble thickly through the slits. Cover the edges of the crust with foil if they are browning too quickly.
8) Cool the pie for 3 hours before serving.