Step 1

Preheat the oven to 350 F (177 C). Lightly grease and line the bottom and long sides of a 9 x 13 inch cake pan with parchment paper.

Step 2

In a large mixing bowl, whisk the all purpose flour, cocoa powder, sugar, baking soda, baking powder and salt until well combined.

Step 3

Whisk in the oil, melted butter, eggs, and buttermilk until well combined. Carefully whisk in the warm water until well combined. Pour the chocolate buttermilk cake into the prepared cake pan.

Step 4

Bake for 30-35 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.

Step 5

Cool the buttermilk cake in the cake pan for 15-20 minutes. Using the parchment paper, gently lift the cake out of the pan to continue cooling on a cooling rack. While the cake cools, make the chocolate buttermilk frosting.

Step 6

Melt the butter in a sauce pan over low heat. Once the butter has melted, whisk in the cocoa powder and cook over low heat for about 1 minute. This helps to bloom the cocoa powder for even more chocolate flavor. Remove the pan from the heat.

Step 7

Whisk in the buttermilk, powdered sugar and vanilla extract until smooth and well combined.

Step 8

Transfer the cooled chocolate buttermilk cake back into the cake pan or onto a serving dish. Pour and spread the buttermilk chocolate frosting onto the cooled cake. Allow the frosting to set, slice the moist chocolate cake and enjoy!