In a baking tray mix apples, sugar and cinnamon and bake for around an hour until they’ve softened and the sugar has melted. Check around halfway through and add a cup of water if things look like they’ll burn. Remove to cool and turn the oven down to 160°C/320°F.
Add the crumble ingredients to a bowl and use your hands to rub the mix until butter has mixed in and the mixture has started to come together into a soft, breadcrumb like texture. Take this and clump it together with your hands into small craggy lumps. Set aside.
Use the food processor to pulse the biscuits with the melted butter and salt until it forms a damp looking, sand-like mixture. Fully line a deep, large rectangular baking tin. Evenly press down the biscuit base until compact.
With a hand whisk (or stand mixer) thoroughly combine cream cheese, mascarpone, vanilla scrapings and caster sugar. One by one add the eggs then thoroughly fold in flour and finally the icing sugar. The resulting mixture shouldn’t be too wet - balance an apple piece on top and see if it sinks. If it does, fold in more icing sugar until a bit stiffer.
Add all the baked apples in a layer then sprinkle over the crumble topping.
Bake for 1 hour 15 minutes. The cheesecake should have risen evenly, have a slight wobble and the crumble should be crunchy and golden. Remove from oven and allow to cool and set for at least three hours in the fridge.