Whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt. Add buttermilk, eggs, and oil to the dry ingredients and mix well until combined.
Slowly add in boiling water and mix to combine. Pour the batter into the prepared pan and smooth the top. Bake about 30 minutes or until a toothpick comes out clean.
Cool in the pan for 5 minutes before removing to cool completely on a wire rack.
Fluffy Buttercream Frosting
Beat butter until fluffy, about 2 minutes on med/high speed with an electric mixer.