Preheat your oven to 350°F (175°C) and grease two 9-inch round cake pans with butter or non-stick spray. Optionally, line the bottoms with parchment paper.

In a large mixing bowl, whisk together 2 cups of all-purpose flour, 3 tablespoons of cornstarch, 2 teaspoons of baking powder, ½ teaspoon of baking soda, and ½ teaspoon of salt until no lumps remain.

In another bowl, cream together ½ cup of butter and ½ cup of vegetable oil with 1 ½ cups of granulated sugar until light and fluffy. Add in 3 eggs, one at a time, followed by 1 cup of milk and 1 teaspoon of vanilla extract, mixing until smooth.

Gradually fold the dry ingredients into the wet mixture until just combined. Divide the batter in half and stir in ½ cup of cocoa powder into one half.

In the prepared cake pans, spoon alternate dollops of the vanilla and chocolate batters to create a marbled effect, being careful not to over mix.

Bake for 30-35 minutes, or until a toothpick inserted comes out clean. Keep an eye on them toward the end for doneness.

Let the cakes cool in the pans for 10-15 minutes before transferring to wire racks to cool completely.

In a mixing bowl, beat 1 cup of softened butter and 4 cups of powdered sugar until smooth. Gradually add ¼ cup of heavy cream and a splash of vanilla until the frosting reaches a spreadable consistency.

Once the cakes are cool, place one layer on a serving plate, spread frosting on top, add the second layer, and frost the top and sides.