Pre-heat oven to 350F (180C) and grease and flour 2 8 inch cake pans.
In a large bowl sift together the flour, corn starch, cocoa, baking soda, baking powder and salt.
Then add the sugar and whisk together, add the eggs, buttermilk, warm water, oil and vanilla beat on medium speed until smooth, approximately 2 minutes.
Divide the batter between the two prepared pans and bake for approximately 30-35 minutes or until toothpick comes out clean. Let cool, then remove from pans.
MASCARPONE CREAM FROSTING
In a medium bowl beat together until very thick the cream and mascarpone. Fold in the Nutella until streaks form. It only takes a 4 or 5 foldings.
PUTTING IT TOGETHER
Remove the tops of the cakes to form flat layers. Place one layer on a plate and top with 1/4 of the frosting, place the other layer on top and spread almost all the remaining frosting (leave approximately 1/2 cup to form rosettes on the top to hold the baci chocolates, I used a 1M tip) over the cake, including the sides. Top with rosettes and Baci chocolates. Enjoy!