Prepare the biscuit base: Preheat your oven to 160°C (140°C fan) and line a 20cm x 20cm square baking tin with baking paper, leaving some overhang on two sides. Place the digestive biscuits inside a sealed food bag and crush them with a rolling pin until they resemble fine, damp sand — you should have no large shards remaining. Tip the crumbs into a bowl, pour over the melted butter, and stir with a fork until every crumb is coated and the mixture feels like wet sand when you pinch it. Press this mixture firmly and evenly into the base of your prepared tin using the flat bottom of a glass. The base should feel compact and solid, not loose. Bake for 10 minutes until it is fragrant and just beginning to turn a deeper gold around the edges. Set aside to cool while you prepare the filling.

Make the cheesecake filling: In a large mixing bowl, beat the room-temperature cream cheese with an electric mixer on medium speed until it is completely smooth and silky — this should take about 2 minutes. Scrape down the sides and the beaters well. Add the caster sugar and beat again for another minute until the mixture looks light and fluffy, with a pale, creamy colour. Add the eggs one at a time, beating on low speed after each addition until just combined — you want to incorporate them without incorporating too much air. Mix in the vanilla extract and the plain flour until the batter looks smooth and uniform, with a thick, mousse-like texture. Finally, gently fold in the double cream using a spatula until the batter is homogenous and glossy. The smell at this stage is wonderfully sweet and dairy-rich.

Cook the spiced apples: Place a medium frying pan over medium heat and add the diced apples, light brown sugar, ground cinnamon, ground nutmeg, and lemon juice. Stir everything together, then let the apples cook for 8–10 minutes, stirring occasionally. You will know they are ready when the apples have softened significantly and the juices have thickened into a golden, syrupy coating that clings to each piece. The colour will deepen to a warm amber, and the kitchen will smell intensely of spiced apple and caramel. Remove from the heat and let the apples cool for 5 minutes before using.

Layer the bars: Pour the cheesecake filling over the cooled biscuit base and spread it gently into an even layer using an offset spatula. The filling should reach right into the corners and sit level. Spoon the cooked apples evenly over the top of the cheesecake, spreading them out so every slice will get a generous portion. Drizzle half of the caramel sauce over the apples in a zigzag pattern. Finally, take a butter knife and gently swirl the caramel into the apples and the very top of the cheesecake filling — just two or three passes, enough to create a marbled effect, but not so much that the layers merge completely.

Bake to perfection: Place the tin in the preheated oven and bake for 40–45 minutes. The edges of the bars will look set and slightly puffed, while the centre should still have a slight wobble when you gently shake the tin — like a well-set jelly. The top will be a pale, golden colour, and you may see a few tiny cracks around the edges, but the centre should remain smooth and unblemished. The aroma coming from the oven will be utterly intoxicating — buttery biscuit, sweet apple, and warm caramel all mingling together. Turn the oven off, crack the door open slightly, and leave the bars inside for 15 minutes to cool gradually. This gentle cooling helps prevent the cheesecake from sinking or cracking.

Cool and refrigerate: Remove the tin from the oven and place it on a wire rack to cool completely at room temperature. This will take about 1 hour — do not rush this step. Once the tin feels cool to the touch, transfer it to the refrigerator and chill for at least 2 hours, ideally overnight. The bars need this resting time to set firmly enough for clean slicing. When fully chilled, the cheesecake should feel firm and resilient when pressed gently with a finger.

Slice and serve: Lift the entire block out of the tin using the baking paper overhang and place it on a chopping board. Use a large, sharp knife to trim the edges for a neat finish, then cut into 12 even bars. Wipe the knife clean between cuts to ensure each slice is pristine. Drizzle the remaining caramel sauce over the bars just before serving, and watch them disappear.