Preheat your oven to 350°F (175°C) and prep three 8-inch cake pans by spraying with non-stick spray and lining bottoms with parchment paper.

Sift together all-purpose flour, unsweetened cocoa powder, baking soda, baking powder, salt, and white granulated sugar in a bowl.

In another large bowl, whisk together large eggs, canola oil, pure vanilla extract, and buttermilk. Gradually mix in hot water.

Pour the wet mixture into the dry ingredients, stirring gently until just combined, then divide the batter into prepared pans.

Bake for 25 to 30 minutes until a toothpick comes out with a few moist crumbs.

Prepare the brownie batter by mixing flour, cocoa powder, cornstarch, and salt, then combine with beaten sugar and eggs, and fold in melted unsalted butter and semi-sweet chocolate chips.

Dollop brownie batter over the cake batter in each pan and swirl for a marbled effect. Bake for an additional 30 to 35 minutes until a toothpick comes out clean.

Let cakes cool in pans for 10 minutes, then invert onto a wire rack to cool completely.

For frosting, sift together powdered sugar and cocoa powder, then beat cream cheese and unsalted butter until fluffy. Mix in sifted ingredients and vanilla.

Level tops of cooled brownie cake layers, layer with frosting, and cover the outside of the cake with remaining frosting.