Preheat oven to 350 degrees. Spray a 9 x 13 inch baking pan with non-stick cooking spray and set aside.

In a large bowl, add the flour, sugar, cocoa baking soda, baking powder, and salt for the cake. Whisk together until combined.

Add the eggs, oil, and buttermilk to the bowl and stir to combine. Add in the hot water and stir just until combined.

Pour batter into the prepared 9 x 13 pan. Bake at 350 degrees for 35-40 minutes until a toothpick inserted in the center comes out clean.

Cool the cake completely.

In another bowl, beat together the frosting ingredients until well combined and fluffy. Spread over cooled cake. Slice to serve. Serves 15.