Preheat your oven to 350 degrees F. In a 9 inch cake pan or spring form pan, spray the bottom with cooking spray, line with parchment paper, and spray again getting the sides this time. Set aside.
In a medium sized bowl, whisk together the flour, salt, cinnamon, and baking powder.
In a large mixing bowl, whisk the butter and sugar by hand vigorously for about 60 seconds. Add the eggs, one at a time, and whisk for 30 seconds after each addition. Slowly mix in the vanilla extract and the buttermilk.
With a rubber spatula, fold the dry ingredients into the wet ingredients. Slowly fold in the flour mixture until there are only small amounts of flour streaks remaining.
Pour the mixture into the prepped cake pan and with the back of a spoon, gently spread the batter to the sides of the pan. Set aside while you make the cream cheese filling.
For the cream cheese filling
In a medium sized bowl, mix the cream cheese with a hand mixer on medium high speed until smooth and creamy.
Add the egg, and mix on high for 30 seconds. Use a rubber spatula to scrape the sides and the bottom of the bowl.
Add the sifted powdered sugar, 1 cup at a time, mixing for 30 seconds after each cup has been added. This should take a little over 1 minute to make.
Once combined, pour the cream cheese mixture onto the top of the cake batter and use a small offset spatula to spread it into an even layer.
Bake for 45-48 minutes, The middle of the cake will still be jiggly but the cake is done when the edges are golden and the middle has cracked.
When the cake is done, let cool for 10-15 minutes, then place in the fridge to chill for at least 2 hours to allow the cream cheese to firm up and set.