Step 1

Preheat oven to 350° F. Grease and flour a 9 x 13-inch baking pan or line with parchment paper. Set aside.

Step 2

In a large mixing bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder and salt. Add the eggs, oil and buttermilk; whisk well to combine. Add the hot water and whisk until the batter is smooth.

Step 3

Transfer the batter to the prepared baking pan. Tap gently on the counter to release air bubbles.

Step 4

Bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean. Cool completely before frosting.

Step 5

Melt the butter in a saucepan over medium-low heat. Whisk in the cocoa powder, cook over low heat for 2 minutes (do not let it boil). Remove from the heat. Add the powdered sugar and buttermilk, whisking until smooth. Add the vanilla; whisk to combine. The icing should be a thick, spreadable consistency, so if you need to thin the icing, add extra buttermilk, one tablespoon at a time.

Step 6

Spread the icing on the cool cake. Let the icing cool and set before slicing and serving.