Line a cupcake pan with paper liners. Preheat oven to 350° F.
In a large bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.
In a second bowl, whisk together eggs, vanilla, sugar, melted butter, sour cream, and milk.
Fold dry ingredients into wet ingredients just until barely combined - don't overmix!
Divide batter evenly amongst prepared cupcake pan, filling each about 2/3 of the way full.
Bake until cake springs back when touched, about 17-20 minutes. Allow to cool completely before frosting.