Preheat oven to 350 degrees F. Position oven rack in middle bottom of oven.

Prepare pan by lightly spraying with baking spray, and lining the bottom with parchment paper.

In large bowl, blend cocoa powder, flour, sugar, baking soda, baking powder, salt with a whisk and mix till combined.

In a separate bowl, whisk together eggs, buttermilk, vegetable oil, vanilla extract, and warm water till well blended.

Pour the wet ingredients into the dry and whisk together until very smooth. Pour into prepared cake pan and bake in preheated oven till a skewer comes out clean, 25-35 minutes.

Sift powdered sugar into a bowl.

Add cream cheese, butter, and peanut butter.

Beat mixture until smooth on low speed using an electric mixer. Set aside.

Warm heavy cream over medium heat till bubbling at the edges.

Pour over chocolate in a bowl and let sit for a minute; then whisk till blended. Let cool till spreadable.

To assemble the cake, remove cooled cake from pan and cut in half horizontally.

Set the top aside, and spread ganache in an even layer over the bottom half of the cake.

Carefully place the top of the cake onto the ganache layer and press it down evenly.

Spread peanut butter frosting over the top of the cake and sides if you desire. Cut into slices and serve.