Preheat the oven to 350 degrees.

Prepare two 9-inch cake pans by coating the inside and sides of the pans with non-stick spray or butter and dusting with flour.

Place parchment paper in the bottoms of both pans.

Set aside.

Add the flour, corn starch, baking powder, baking soda and salt to a large mixing bowl and whisk to combine. Set aside.

In a large mixing bowl, add the butter and sugar and use a paddle attachment to cream together on medium speed until light and fluffy. Approximately 2-3 minutes.

Add the eggs one at a time, mixing well in between.

Add in the vanilla.

With the mixer on low speed, alternate by adding 1/3 of the dry ingredients to the mixture, then ¾ cup of the buttermilk, followed by another 1/3 of the dry ingredients, then the remaining ¾ cup of the buttermilk, then the remaining dry ingredients. Mix until there are no more flour streaks, then stop. Do not overmix.

Divide the batter roughly in half.

Add the chopped chocolate to a microwave safe bowl and melt in 20 second intervals, stirring in between, until the chocolate is melted and smooth. Watch closely to ensure you don’t burn the chocolate.

Add the chocolate to ½ of the batter and whisk until fully incorporated.

Alternate adding ¼ cup scoops of vanilla batter and then chocolate batter in a checkered pattern, dividing the batter evenly between the two pans. Tap the pans gently to settle the batter.

Use a butter knife to gently swirl the batter. Do not over swirl or the cakes will start to combine, and you will lose the marble pattern.

Bake the cakes in the center of the oven for 25-35 minutes, or until a toothpick inserted into the center of both pans comes out free of batter, but with a few crumbs sticking to it. Do not overbake.

Remove the cakes from the oven and allow them to cool for 10 minutes before flipping them onto a wire rack to cool completely before frosting.

When ready to frost, add the room temperature butter to a large bowl and beat the butter with the paddle attachment for 2-3 minutes until smooth and creamy.

Add the sifted cocoa powder and salt and mix on low until just combined.

With the mixer on low, add the powdered sugar ¼ cup at a time until everything is combined.

Then increase the speed to medium and add in the cream and vanilla and mix until smooth and well-combined.

To assemble, place one cake layer on a cake stand or plate and spread ½-3/4 cup of frosting evenly across the top.

Place the second layer on top and spread a very thin coating of frosting around all surfaces to seal in the crumbs. Allow the cake to rest until the frosting is set.

Add the remaining frosting to the top and sides of the cake and use an offset spatula to create swirls across the surface. Chill for 30 minutes, then serve.