Preheat the oven to 350F. Spray three 8-inch cake pans with baking nonstick spray. Line the bottoms with 8-inch parchment paper circles and spray again.
In a large bowl, sift the flour, cocoa powder, cornstarch, baking powder, baking soda, and salt. Set aside.
2 cups All-purpose flour, 1 cup Unsweetened cocoa poweder, 2 tsp Baking powder, 1/2 tsp Baking soda, 1 tsp Salt, 1/4 cup Cornstarch
Start heating the water on the stove until streaming. In a separate bowl, mix the oil, sugar, vanilla, eggs, and buttermilk. Slowly add in the hot water. Make sure to add it in slowly to not cook the eggs.
1 cup Oil, 1 tsp Pure vanilla extract, 4 Large eggs, 1 cup Buttermilk, 1 cup Hot water, 1 3/4 cup White granulated sugar
Pour the wet ingredients into the dry and mix until just combined. Pour the cake batter evenly into the three cake pans.
Bake the cakes for 25-28 minutes. Bake until toothpick inserted comes out clean.
Let the cakes sit in the hot pans for 10 minutes. Then, transfer to a cooling rack to cool completely.