Preheat your oven to 325 and spray your donut tins with cooking spray!
First off, melt your butter so that it can begin to cool. Next mix together the milk and cream of tartar.
Mix together the dry ingredients, flour, cacao powder, baking soda, salt, cinnamon and brown sugar.
In a separate bowl mix together the milk and cream of tartar, butter, and vanilla.
Combine the wet and dry ingredients then pour the batter into the donut pans and bake for 11-13 minutes until a toothpick comes out clean. Don't overfill the pans as you could result in full pans and no donut hole!
Allow to rest for 5 minutes before inverting onto a wire rack to cool. While cooling make the glaze by mixing the powdered sugar, cacao powder, cinnamon, vanilla, then 4 tablespoons of milk.
Dip the cooled donuts then sprinkle them, allow to cool so the glaze hardens some, and enjoy!
Notes
You can opt to make these without the cinnamon if you prefer. I like the extra notes and how cinnamon and chocolate go together!