Whipped Chocolate Ganache: In a pot, heat up the cream until simmering. In a bowl, add in the milk and dark chocolate, and pour in the hot cream. Let the mixture sit for 5 minutes and then whisk well until the mixture is homogenous. Leave in the fridge to set for at least 5 hours or best overnight. Once completely set, use an hand-held mixer and whisk the ganache until it's whipped.
Salted Caramel: warm up the cream in a microwave or pot. In a separate heavy duty pot, add the white sugar and water, stir until the mixture is combined. Turn the heat on to a medium and let the sugar mixture cook and turn amber. If there is hardened sugar on the sides of the pot, get a wet brush and carefully remove it from the sides. You can occasionally swirl but do not stir. Once the caramel has reached a nice amber colour, add in the warm cream and whisk well until combined. Add in the butter and whisk until melted and glossy. Stir in the sea salt and vanilla. Set aside until completely cooled.
Biscuit Top: Mix 250g of the Digestive/Graham biscuit crumbs with 90g of melted butter until it looks like wet sand. Place a piece of parchment paper on top of a chopping board and then place your cheesecake tin (without the tin base) onto the parchment paper and chopping board. Pour the biscuit mixture into the tin, spread and press down firmly until it forms a nice even round base. Carefully lift up the cheesecake tin to reveal the round pressed crust and place into the fridge to set.
Biscuit Base: Mix 500 g Digestive/Graham biscuits, crushed with 180 g unsalted butter, melted until it looks like wet sand. Press firmly into the base of a 23cm x 7cm springform tin. Chill while you make the filling.
Whipped Cream: In a bowl, add in the cream and sugar, and beat until stiff peak.
Assemble: add half the whipped cream into the bottom of the biscuit base and spread out evenly. Pipe the whipped chocolate ganache on top of the whipped cream and drizzle over with the salted caramel. Lay on the banana slices and top with the remaining whipped cream. Place the biscuit top over the whipped cream to close the pie and place the pie back into the fridge to set for at least 4 hours or overnight.
Unmould and serve! If you have difficulties unmoulding the pie, use a blow torch to lightly heat up the edges of the springform tin.