• Preheat the oven to 325 degrees and line three 6-inch cake pans, two 8-inch cake pans, or two 9-inch cake pans with parchment paper. Then spray with non-stick spray. Set aside.

Chocolate Cake

• Whisk together the flour, cocoa powder, sugar, baking soda, baking powder, and salt in a large bowl. Set aside.
• In a medium-sized mixing bowl, whisk together the warm water, milk, eggs, vegetable oil, and vanilla extract until combined. Slowly add the wet ingredients into the dry, whisking until a wet batter forms (do not overmix).
• Pour the batter evenly between the prepared cake pans and bake for 32-35 minutes, or until a toothpick inserted into the middle of the cakes come out clean. Allow the cakes to cool in the pans for 5 minutes then carefully remove them from the pans and cool on a wire rack. Let the cakes cool completely before frosting.

Chocolate Buttercream

• In the bowl of an electric stand mixer with the paddle attachment, beat the butter on med-high speed until creamy (about 1-2 minutes). Add the powdered sugar, cocoa powder, heavy cream, and vanilla extract and mix on low speed until combined (about 30 seconds). Then increase the speed to high and beat for another 1-2 minutes (frosting should be light and creamy).

Assemble

• If needed, use a serrated knife to level off the tops of each cake layer to create a flat surface. Place one cake layer on a cake stand or plate and evenly cover it with chocolate buttercream (I like to use my offset spatula for this part). Place the next cake layer on top and repeat until each layer is frosted.
• Give the entire cake a crumb coat (see note below) by spreading a thin layer of buttercream around the sides and top of the cake. Place the entire cake in the refrigerator for 10 minutes.
• Remove the cake from the refrigerator and finish frosting with the remaining buttercream. Cover the sides and top of the cake again until frosted to your desire (use a cake scraper for a smooth finish if desired).