Preheat your oven to 350F and prepare two 4-inch cake pans with butter or parchment paper.
In a bowl, whisk together sugar, flour, cornstarch, baking powder, baking soda, and salt until smooth.
Add oil, melted butter, vanilla, egg white, buttermilk, and red food color to the same bowl. Gently whisk until well combined.
In a separate bowl, mix cocoa powder with hot water to bloom it, then add to the cake batter and gently mix.
Divide the batter evenly between the two cake pans.
Bake for approximately 15 minutes or until the cakes are fully cooked.
Allow the cakes to cool completely.