Preheat your oven to 165°C (330°F) with the fan on for even heat distribution. Grease and line two 8-inch round cake pans with parchment paper.

In a mixing bowl, sift together the all-purpose flour, cornstarch, baking soda, baking powder, and salt.

In a separate large bowl, combine the room-temperature unsalted butter, vegetable oil, and granulated sugar. Beat on medium speed until light and fluffy, about 3–5 minutes.

Add the large eggs, one at a time, mixing well after each addition until the mixture is smooth and creamy.

Incorporate the vanilla extract, white vinegar, and half of the buttermilk into the batter. Mix on low speed until just combined.

Gently fold in half of the dry mixture using a spatula into the wet batter until almost incorporated. Then add the remaining buttermilk and the rest of the dry mixture, folding carefully until just combined.

Pour the cake batter evenly into the prepared pans, smoothing the tops with a spatula. Bake for about 30 minutes or until a toothpick inserted in the center comes out clean.

Once baked, let the cakes cool in the pans for 15–20 minutes before transferring to wire racks to cool completely.