Whisk the flour, cocoa powder, baking powder, baking soda, and salt together in a large bowl until thoroughly combined. Set aside
In a medium bowl, whisk the eggs, granulated sugar, brown sugar, oil, and vanilla together until combined.
Pour half of the wet ingredients into the dry ingredients. Then half of the buttermilk. Gently whisk for a few seconds. Repeat with the remaining wet ingredients and buttermilk. Stir until just combined, do not overmix. The batter will be thin.
Pour or spoon the batter into the liners. Fill only halfway
Bake for 18-21 minutes, or until a toothpick inserted in the center comes out clean. Allow to cool completely