Preheat the oven to 325 degrees.
Combine the flour, cocoa powder, baking soda, baking powder and salt in a medium bowl.
In a small bowl, mix the brown sugar, buttermilk, eggs, butter and vanilla.
Create a well in the center of the dry ingredients.
Add the wet ingredients to the dry ingredients and mix well.
Spray your doughnut pan lightly with non-stick spray.
Fill each doughnut well 2/3 full with batter. (I use a pastry bag with a 2A tip to do this)
Bake for 13 minutes, or until the doughnut springs back when touched lightly with a finger.
Remove to a cooling rack right away.