Preheat the oven to 350F degrees. Spray a 6 cavity doughnut pan with non-stick cooking spray.
In a medium bowl whisk together the flour, cocoa, baking soda and salt.
In a separate medium bowl whisk together the melted butter, egg, sugars, vanilla & buttermilk.
Add the dry ingredients into the wet & whisk until combined. The batter will be thick.
Spoon the batter into the prepared doughnut pan. Or pour the batter into a ziplock bag, cut off the bottom corner, and pipe the batter into the prepared tin.
Bake for 8-10 minutes. If you lightly touch the doughnut, it should spring back. Or an inserted toothpick should come out clean.
Allow doughnuts to cool in the pan for 5-10 minutes, then remove from the pan and continue cooling on a wire rack
While the doughnuts are cooling, make the glaze. Whisk together the icing sugar, cocoa and about 2 tablespoons cream. Add the corn syrup and slowly add the remaining cream until the glaze is smooth.
Once the doughnuts are cooled, dip the top in the glaze and sprinkle with sprinkles.