Prepare the Cake:

1. Preheat the oven to 350°F (175°C). Grease and flour two 9-inch round cake pans or line them with parchment paper for easy release.

Mix the Dry Ingredients:

1. In a large mixing bowl or stand mixer, combine the flour, sugar, cocoa powder, baking soda, baking powder, and salt. Whisk together to ensure even distribution of the dry ingredients.

Add Wet Ingredients:

1. Add the eggs, buttermilk, sour cream, warm water, vegetable oil, and vanilla extract to the bowl. Mix on medium speed for about 2 minutes until the batter is smooth and fully combined. The batter will be slightly thin, which is ideal for a moist cake.

Divide and Bake:

1. Evenly distribute the batter between the two prepared cake pans. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean.

Cool the Cakes:

1. Allow the cakes to cool in their pans for 10 minutes. Then, carefully transfer them onto a wire rack to cool completely before frosting.

Prepare the Frosting:

Cream the Butter and Cream Cheese:

1. In a stand mixer fitted with a paddle attachment, beat the softened butter and cream cheese together on medium-high speed for 2 minutes or until the mixture becomes light and fluffy.

Add Cocoa and Vanilla:

1. Mix in the unsweetened cocoa powder, vanilla extract, and a pinch of salt. Blend until fully combined.

Incorporate Powdered Sugar:

1. Gradually add the powdered sugar while mixing on low speed. Once the sugar is fully incorporated, add the milk, one tablespoon at a time, until you achieve a creamy yet spreadable frosting consistency. If the frosting becomes too thin, add a bit more powdered sugar.

Assemble the Cake:

Layer the Cake:

1. Place the first cake layer on a serving plate. Spread a generous layer of frosting evenly across the top.

Add the Second Layer:

1. Place the second cake layer on top and spread another thick layer of frosting over the top and sides of the cake. Smooth it out using an offset spatula.

Chill Before Serving:

1. For best results, refrigerate the frosted cake for 30 minutes to allow the frosting to set before slicing. However, it can be served immediately if desired.