Preheat your oven to 350°F (175°C) and prepare three 8-inch round cake pans with baking spray and parchment circles.

In a large mixing bowl, sift together flour, cocoa powder, baking soda, baking powder, salt, and sugar.

In another bowl, whisk together eggs, oil, vanilla, and buttermilk, then gradually stir in hot water.

Fold the wet mixture into the dry ingredients until just combined, then divide the batter among the prepared pans.

For the brownie layer, mix flour, cocoa powder, cornstarch, and salt in a bowl, then whisk eggs and sugar for 5 minutes until thick.

Gently fold the flour mixture into the whipped egg mix, then add chocolate chips and fill the same pans.

Bake for 30 to 35 minutes, checking doneness with a toothpick. Cool in pans for 10 minutes before transferring to wire racks.

Beat cream cheese and butter until smooth, then add sifted cocoa powder and powdered sugar until fluffy.

Trim the domes off cooled cake layers, stack them with frosting between layers and cover the whole cake with remaining frosting.

Chill in the refrigerator for 30 minutes to set the frosting, then slice and serve.