Preheat the oven to 350 degrees F. Line a muffin tin with liners. Set aside.
In a medium bowl, whisk together the cake flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In the bowl of a stand mixer, cream the butter and sugars together. Add the eggs, one at a time, mixing well between additions. Add the vanilla extract.
Alternate between adding some of the dry ingredients with the buttermilk. After the last addition, mix until just combined. Scrape down the sides, making sure to get the bottom, too. Mix for another minute.
Fill the liners ½ of the way full. Bake for 20-25 minutes or until a knife/toothpick, when inserted into the center, comes out clean.
Allow the cupcakes to cool for 5-10 minutes in the muffin tin, then remove and place them on a wire rack to finish cooling completely.