• Preheat the oven to 355°F (180°C/160°C fan). Grease the sides and line the bottom of a 20 cm (8-inch) or 23 cm (9-inch) springform pan with parchment paper.

For the biscuit crust:

• Place the digestive biscuits into a food processor and blitz into fine crumbs. Add the melted butter and whizz again until you have the desired crumbly consistency. It should resemble damp sand.
• Pour the biscuit mixture into the prepared pan and use a glass (or the back of a spoon) to pat it into a smooth and compact layer on the base and up the sides. Cover and chill in the fridge while you make the filling.

For the cinnamon-spiced apples:

• Add the butter to a large non-stick frying pan placed over low-medium heat. Once foaming, add the cubed apples, followed by the sugar and cinnamon. Stir gently to coat the apples in the cinnamon and sugar.
• Cover and cook gently for about 10 minutes - or until the apples are tender. Taste and adjust the sugar/cinnamon, as necessary. Remove from the heat and set aside. 

For the cheesecake filling:

• Place the cream cheese into a large mixing bowl and beat until smooth and creamy. Add the superfine (caster) sugar and beat again. Gradually add the eggs, one at a time, beating until combined.
• Gently mix in the vanilla extract, followed by the sour cream and cornflour, until you have a smooth cheesecake filling. Take care not to overmix. Set aside.

For the crumble topping:

• In a large mixing bowl, add the flour, sugar, oats, cinnamon, and a pinch of salt. Rub in the butter until you have a crumbly consistency. 

Bake the cheesecake:

• Remove the chilled biscuit crust from the fridge and set onto a baking tray. Pour the cheesecake filling into the tin and smooth over the top. Spoon over the cinnamon-spiced apple pieces (you want them to be evenly distributed across the cheesecake). Sprinkle with the crumble topping. 
• Bake in the preheated oven for about 35-40 minutes - or until just set and it no longer wobbles in the middle. Take care, as the time will vary depending on whether you used an 8-inch or 9-inch pan - try not to overbake it, as it will continue to cook as it cools. 
• Once ready, turn off the oven and leave the cheesecake to cool inside with the door slightly ajar for at least 1 hour. Next, remove from the oven and leave to cool completely before covering and chilling for at least 6 hours, ideally overnight, until firm.

Meanwhile, make the salted caramel sauce:

• Add the sugar to a medium-sized heavy-based saucepan and place over a medium heat. Stir occasionally at first, then just swirl the pan to ensure it melts evenly (otherwise it will start clumping).
• Once the sugar has melted, continue to bubble over medium heat until it turns a gorgeous amber color - watch closely (this will only take 1 minute or so) as you don’t want it to burn and become bitter.
• Remove from the heat and quickly add the butter. Whisk for about 30 seconds until completely smooth. Pour in the double cream and whisk again until smooth and glossy. Finally, whisk in the vanilla extract and salt. Pour into a jug. If making ahead of time, leave to cool completely before covering and chilling in the fridge for up to 3 days. Reheat gently in the microwave or on the stove.
• When ready to serve, remove from the tin and set onto a flat plate. Cut into slices and serve drizzled with warm salted caramel sauce.