Preheat your oven to 350°F (175°C). Grease and flour a 9x5-inch loaf pan.
In a medium bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, cream the softened butter and sugar together until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk. Start and finish with the dry ingredients, mixing until just combined.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 60-70 minutes, or until a toothpick inserted into the center comes out clean.
Let the cake cool in the pan for 10 minutes, then transfer it to a wire rack to cool completely.