Preheat the Oven:
Preheat to 350°F (175°C). Line the bottom of a 9×13-inch baking dish with parchment paper.

Prepare the Shortbread Crust:
In a food processor, pulse together flour and brown sugar until combined.
Add cold butter (cut into tablespoons) and pulse until fine crumbs form.
Press the mixture firmly into the prepared pan and bake for 20 minutes, until lightly golden.

Make the Cheesecake Layer:
In a large bowl, beat the cream cheese until light and fluffy.
Add granulated sugar and beat until smooth.
Mix in vanilla, sour cream, and heavy cream. Stir in flour.
Gently stir in eggs, one at a time, just until combined (do not overmix).
Pour the cheesecake batter over the baked crust.

Add the Apple Layer:
In a separate bowl, toss the diced apples with sugar, cinnamon, and flour.
Evenly sprinkle the apple mixture over the cheesecake layer.

Make the Streusel Topping:
In a food processor, combine flour, baking powder, and brown sugar.
Add butter in small pieces and pulse until crumbly.
Sprinkle with heavy cream and pulse once or twice to create small clumps.
Evenly sprinkle the streusel over the apple layer.

Bake:
Bake for 45 minutes at 350°F.
Turn off the oven and let the bars sit inside (door closed) for 20 minutes.
Then, crack the oven door and allow the bars to cool completely at room temperature.

Chill and Serve:
Refrigerate for at least 3 hours before slicing into bars.
Drizzle with caramel sauce before serving, if desired.