Preheat your oven to 350°F and prepare two 4-inch cake pans by greasing them or lining them with parchment paper.
In a bowl, whisk together the sugar, flour, cornstarch, baking powder, baking soda, and salt until well combined and no lumps remain.
Add the oil, melted butter, vanilla extract, egg white, buttermilk, and red food coloring to the dry ingredients. Gently whisk until combined.
In a separate small bowl, mix the cocoa powder with the hot water until smooth. Add this mixture to the cake batter and gently fold it in.
Divide the batter evenly between the two cake pans.
Bake for approximately 15 minutes or until the cakes are cooked through. Allow them to cool completely.