Make the cookie dough

1. Preheat oven to 350°F (180°C). Line a 9×13-inch pan with parchment paper that comes up above the long sides of the pan (they’ll be used to lift the bars out of the pan later) and use baking spray to spray the short sides. Set aside.
2. Combine the flour, baking soda, cinnamon and salt in a medium sized bowl and set aside.
3. Cream the butter and sugars together in a large mixer bowl on medium speed until light in color and fluffy, about 2-3 minutes. Scrape down the sides of the bowl a few times to be sure all is well incorporated. You should be able to see the change in color and texture happen and know it’s ready.
4. Add the eggs one at a time and mix until well combined after each.
5. Add the vanilla extract and mix until well combined.
6. Add the dry ingredients and mix until the dough is just combined. Do not over mix.
7. Stir in the oats. Dough will be thick, but sticky.
8. Press half of the cookie dough evenly into the bottom of the prepared cake pan. Set the remainder of the cookie dough aside.

Make the cheesecake layer and bake

1. Add the cream cheese and sugar to a large mixer bowl and beat until smooth and creamy.
2. Add the egg yolk and mix until well combined. Add the egg white and mix until well combined. They are added separately to prevent the filling from getting lumpy.
3. Add the cinnamon and vanilla extract and stir until well combined.
4. Spread the cheesecake mixture evenly over the oatmeal cookie base.
5. Toss the chopped apples with the cinnamon and nutmeg, then sprinkle apples evenly over the cheesecake mixture and crumble the remaining cookie dough on top.
6. Bake for 30-35 minutes, or until golden brown on top. They may jiggle a bit, but should look set.
7. Set on a cooling rack to cool to room temperature, then refrigerate until cold and firm.
8. Cut into bars and serve. Store bars in an air-tight container in the fridge. Best if eaten within 4-5 days.