Prepare Apple Filling: In a bowl, combine diced Granny Smith apples with sugar, cinnamon, nutmeg, and salt. Let this mixture sit for 30 minutes to allow the flavors to meld and the apples to soften slightly.

Make Shortbread Crust: Preheat your oven to 350°F. In a mixing bowl, cream together butter and sugars until light and fluffy. Gradually mix in the flour and salt until combined. Spread this mixture evenly into a lined 9x13 baking pan and bake for 15 minutes until set but not fully cooked.

Prepare Cheesecake Filling: In another bowl, beat the softened cream cheese, granulated sugar, and vanilla extract until smooth and creamy. Add in the eggs one at a time, mixing just until smooth. Set this glorious filling aside.

Create Streusel Topping: In a separate bowl, combine softened butter, brown sugar, flour, and cinnamon. Use your fingertips to mix until crumbly, resembling wet sand, and set aside.

Assemble Bar Layers: Pour the cheesecake filling over the shortbread crust, smoothing it gently. Evenly spread the apple mixture on top, followed by a generous sprinkle of streusel topping.

Bake: Place in the oven and bake for about 35 minutes until the filling is set, and the top is a lovely golden brown. Allow the bars to cool completely before slicing, ideally refrigerating for at least 4 hours for the best texture.

Optional: Drizzle with warm caramel sauce just before serving for an extra touch of sweetness.