Preheat your oven to 350°F (175°C).
In a bowl, mix flour, cocoa powder, sugar, baking powder, baking soda, and salt.
In another bowl, whisk buttermilk, vegetable oil, egg, and vanilla.
Combine wet and dry ingredients until just mixed.
Pour batter into a greased donut pan.
Bake for 10-12 minutes.
Let cool before removing from the pan.
