Preheat your oven to 350°F (conventional).

In a bowl, sift together flour, cornstarch, baking powder, baking soda, and salt. Give it a good mix and set it aside.

In another bowl, whisk together sugar, oil, and melted butter for 1-2 minutes until it changes color. Add the eggs, egg white, and vanilla, whisking for another 1-2 minutes.

Alternate adding a third of the buttermilk and dry ingredients to the wet mix, gently folding until everything is combined.

Prep your bundt pan by generously brushing it with oil and dusting with granulated sugar. Pour in the batter.

Bake for around 30 minutes (keep an eye on it!) until a toothpick comes out with moist crumbs attached.

Let the cake chill in the pan for 10-15 minutes, then carefully flip it out.

Sprinkle some powdered sugar on top, and you're ready to savor the deliciousness!