In a medium bowl, whisk together flour, cornstarch, baking powder and salt. Sit aside.
In the bowl of a stand mixer add butter, cream cheese, granulated sugar, and brown sugar. Beat until mixture has lighten and is fluffy. About 3-5 minutes.
Add eggs one at a time, making sure each is incorporated before adding the next.
Add vanilla extract, mix thoroughly.
Add dry ingredients, alternating with buttermilk until incorporated. Mix for about 1-2 minutes total.
Bake at 350F for 55-60 minutes. Baking time may vary depending on your oven and pan size. You'll know the cake is done when the middle springs back when you press it, or if a toothpick can be inserted and comes out clean.
Let the cake cool completely