For the pastry, sift the flour and salt into a mixing bowl. Rub the butter into the flour until the mixture resembles breadcrumbs. Add the lightly beaten eggs a little at a time, mixing until the dough just comes together (you may not need all the eggs). Knead lightly until it forms a smooth ball, then wrap in cling film and place in fridge for 45 minutes.
Pre-heat oven to 180C/350F/Gas 4. Lightly grease a 29cm/11½in pie tin.
For the blueberry jam, place the blueberries, apple juice, sugar, vanilla and cinnamon into a saucepan and bring to the boil. Reduce the heat and simmer for four minutes. Stir in the pectin and cornflour. Cook for one minute then remove from the heat and allow to cool slightly.
On a lightly floured surface roll out the pastry to a thickness of 0.5cm/¼in. Roll the pastry up over the rolling pin and transfer it to the greased tin. Gently push the pastry into the tin.
Place a square of baking parchment into the pastry shell, fill with baking beans and bake ‘blind’ for 15 minutes. Remove the paper and the baking beans and return the pastry case to the oven for 10-12 minutes until light golden-brown. Place the tin onto a cooling rack and set aside to cool completely.
For the raspberry chiffon filling, place the raspberries, sugar and lemon juice in a small pan and bring to the boil for 3-4 minutes. Strain the raspberries through a sieve into a bowl, pressing the fruit through the sieve with the back of a wooden spoon.
Remove the gelatine from the soaking water, squeeze and whisk into the raspberry mixture. Allow to cool slightly, then whisk in the whipped cream. Pour the chiffon filling into a large tray to cool. Check every 15-20 minutes until it is semi-set – this should take about an hour.
Spread the blueberry jam evenly across the base of the cold pastry case. Place in the fridge to set.
For the chantilly cream, chill a glass mixing bowl for 10-15 minutes in the fridge (both the cream and bowl should be very cold). Using a handheld electric mixer, whip the cold cream until soft peaks form when the whisk is removed. Sift in the icing sugar, add the vanilla and beat to combine. Do not overbeat as chantilly cream should be quite soft. Transfer the cream to a piping bag fitted with a large star nozzle and refridgerate.
When raspberry chiffon filling has thickened but is still pourable, pour it into the pastry case and smooth the top with a palette knife. Place the pie in fridge for 20-30 minutes or until the chiffon has fully set.
For the raspberry coulis, place the raspberries, sugar and 100ml/3½fl oz water into a small saucepan and gently bring to the boil. Simmer for four minutes, then press the fruit through a fine sieve into a mixing bowl. Return the fruit purée to the saucepan and stir in the cornflour. Bring the mixture to a simmer, stirring constantly, until thickened. Set aside to cool. Repeat the process for the blueberry coulis.
When the chiffon filling has set, pipe rosettes of chantilly cream on top, creating concentric circles, starting from the outside edge and working inwards.
Transfer the raspberry coulis to a piping bag fitted with a small plain nozzle, and pipe a swirl of coulis onto half the rosettes. Repeat the process with the blueberry coulis on the remaining rosettes.
Place a blueberry or raspberry onto each rosette with the matching coulis. Chill until ready to serve.