In a large bowl, beat together butter and sugar until light and fluffy. Add in eggs and vanilla, mixing well to combine. In a separate bowl, combine flour, cocoa powder, baking soda, baking powder and salt. Add half a dry ingredients to wet ingredients and mix well to combine, followed by half of buttermilk, mixing well to combine beating well after each addition. Add remaining dry ingredients, mix well, and finish with remaining buttermilk, mixing well to combine.