Preheat the oven to 350.
Spray a 6-cavity doughnut pan with cooking spray.
In a medium mixing bowl whisk flour, cocoa, baking soda and salt.
In a separate medium-sized bowl, whisk the melted and cooled butter, egg, sugars, vanilla and buttermilk until thoroughly combined.
Add the dry ingredients to the butter mixture.
Whisk ingredients until combined, but DO NOT OVERBEAT.
The batter will be thick.
Spoon the batter into a ziplock bag.
Cut off the bottom corner, then pipe the batter into the greased doughnut tin.
Bake for 8-10 minutes at 350 degrees, until donut is set or a toothpick inserted in center comes out clean.
If you lightly touch the doughnut, it should spring back.
Allow doughnuts to cool in the pan for 5-10 minutes.
Remove from the donut pan and continue cooling donuts on a wire rack.
While the doughnuts are cooling, make the glaze.
Dip donuts into glaze and immediately sprinkle with sprinkles so they adhere.