Preheat your oven to 350°F (175°C) and prepare the baking pan.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition, followed by the vanilla extract.
Alternately add the dry ingredient mixture and buttermilk to the batter, starting and ending with the dry ingredients.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 50-60 minutes, checking for doneness with a toothpick inserted in the center.
Allow the cake to cool in the pan for 15 minutes before transferring it to a wire rack.
Once completely cooled, frost or dust with powdered sugar as desired before slicing.