Preheat oven to 350.
Cut softened butter into cake mix, add the egg and mix with a hand mixer on low until smooth.
Pat into a square 8x8 baking sheet lined with parchment paper.
In a separate bowl, mix cream cheese, 2 eggs, powdered sugar, vanilla and salt until smooth.
Pour over first layer, bake for 35 minutes.
Allow to cool completely before cutting into squares.
