Make the Streusel:
Preheat your oven to 350°F (175°C). Grease and line an 8×8-inch square baking pan with parchment paper, leaving some overhang on two sides for easy removal.
In a bowl, mix the cold, cubed butter, brown sugar, salt, flour, oats, and cinnamon. Once combined with small clumps, set aside in the fridge for later.
Make the Crust:
Cream together flour, both sugars, vanilla extract, salt, and softened butter until a soft cookie dough forms.
Spread the cookie dough on an 8×8-inch pan lined with parchment paper. Press to form an even layer and bake for 13 minutes.
Make the Cheesecake Filling:
In a separate bowl, beat softened cream cheese, heavy cream, granulated sugar, flour, and vanilla extract until smooth. Mix in the egg.
Spread the cream cheese filling evenly over the warm sugar cookie crust.
Make the Apple Mixture:
Toss diced apples with ground cinnamon, 1 tablespoon of granulated sugar, and lemon juice. Spread the apple mixture evenly over the cream cheese layer.
Sprinkle the prepared streusel topping over the apples, covering them evenly.
Bake for 35-40 minutes until the edges are golden brown, and the center is set.
Cool completely in the pan on a wire rack. Refrigerate for at least 2 hours to allow them to set.
Once chilled, use parchment paper overhangs to lift the bars out of the pan. Place them on a cutting board and slice into squares.
Enjoy as is or with a caramel drizzle on top. Savor the deliciousness of fall!