Preheat the oven to 170C or 150C if using a fan oven. Place a deep tray on the bottom shelf of the oven and fill half-way with boiling water.
Line the base of a 23cm loose bottomed springform tin with parchment paper and wrap two layers of foil around the outside of the tin to prevent any leakages.
Blend the biscuits in a food processor until smooth and add the melted butter.
Press the biscuit crumb into the base of the tin. Chill in the fridge.
For the Cheesecake:
In a large bowl, whisk together the cream cheese, vanilla, and all but 1tbsp of sugar. Once smooth, add the egg yolks one by one, beating well between each addition.
Melt the milk and dark chocolates, and heat the cream until hot. Mix together.
In a separate bowl or the bowl of a stand mixer, whisk the egg whites with the reserved tbsp of sugar to soft peak.
Fold the melted cream and chocolate into the cream cheese mix, whisking well to combine. Whisk in a third of the egg whites to loosen, then fold in the remaining whites. Sprinkle in the cornflour, and fold through. Pour the cheesecake mix into the chilled base and smooth the top.
Place the tin in the tray with the boiling water and bake the cheesecake for 1 ½ hours until the edges are set but the centre has a slight wobble. Remove from the oven and leave to cool completely in the tin, for at least 2 hours or overnight.
For the Caramel Ganache:
Heat the cream in a medium saucepan over a medium heat until it reaches boiling point. Remove from the heat and set aside.
Make a caramel by placing the sugar in a clean saucepan over a medium heat, swirling occasionally, until golden brown. Add the butter, taking care as the caramel will bubble.
Reduce the heat to low and slowly pour in the warm cream, whisking all the time. Add the salt.
Bring the sauce back to the boil, and pour over the chocolate, stirring to melt completely.
Leave the sauce to cool in the fridge, and after 2-3 hours it will have reached a soft scoopable consistency. Whisk the ganache until lighter in volume, pale and soft and set aside until ready to assemble the cheesecake.
Unmould the cheesecake from the tin. Spread the whipped caramel ganache over the cooled cheesecake, and decorate with caramel sauce and shaved chocolate to serve.