Prepare the pan: Preheat the oven to 165°C / 325°F. Line a 9 × 13-inch pan with parchment paper, leaving an overhang for easy removal.

Make the crust: Combine the graham cracker crumbs, brown sugar, melted butter, and salt. Mix until evenly moistened. Press firmly and evenly into the base of the prepared pan.

Pre-bake: Bake the crust for 8 minutes. Remove and allow to cool slightly while preparing the filling.

Prepare the apples: Melt the butter in a small pan over medium heat. Add the diced apples, brown sugar, and cinnamon. Cook for 3–4 minutes, stirring gently, until the apples are just beginning to soften. Do not overcook. Remove from the heat and cool completely.

Prepare the cheesecake: Beat the cream cheese and sugar on medium speed until smooth and creamy. Add the eggs one at a time, mixing just until incorporated after each addition. Add the sour cream, vanilla, flour, and salt. Mix until smooth, taking care not to overbeat.

Assemble: Gently fold the cooled apples into the cheesecake mixture. Pour evenly over the pre-baked crust and smooth the surface.

Make the oat crisp: Combine the oats, flour, brown sugar, and cinnamon. Add the cold cubed butter and rub or pinch together until coarse, irregular crumbs form. Scatter evenly over the cheesecake layer.

Bake: Bake for 42–50 minutes, until the edges are set and lightly puffed while the centre still has a slight wobble.

Cool and chill: Cool completely at room temperature, then refrigerate for at least 4 hours, preferably overnight, until fully firm.

Cut: Lift the chilled cheesecake from the pan using the parchment overhang. Cut into 12 even bars using a sharp knife. Wipe the knife clean between cuts for a neat finish.

Finish: Warm the caramel sauce until pourable but not hot. Drizzle over the cut bars, allowing some caramel to run naturally down the sides. Finish with a light sprinkle of flaky sea salt.