Preheat the oven to 350℉. Spray three 8-inch cake pans with baking spray. Line the bottoms with parchment paper circles and spray again.
In a medium bowl, sift the flour, cornstarch, baking powder, baking soda, and salt. Set aside.
2 1/2 cups All-purpose flour, 1/4 cup Cornstarch, 1 tsp Baking powder, 1/2 tsp Baking soda, 1 tsp Salt
Heat boiling water on the stove. In a small bowl, add the chopped chocolate and cocoa powder. Pour the hot water over the chocolate and cover with a kitchen towel and let it sit for 5 minutes. Then, stir it well so there is no more lumps.
4 oz Milk chocolate bar, 1/3 cup Unsweetened cocoa powder, 1/2 cup Boiling water
In a large bowl, add oil, sugar, vanilla, eggs, and buttermilk and mix. Add the chocolate and mix it in. Add the dry ingredients and mix well until no more lumps remain.
1 cup Oil, 1 3/4 cup White granulated sugar, 1 tsp Pure vanilla extract, 4 Large eggs, 1 cup Buttermilk
Separate the cake batter between the three cake pans. Bake for 22-28 minutes until a toothpick inserted comes out clean.
Let the cakes sit in the hot pans for 10 minutes. Transfer to a cooling rack and cool completely before decorating.