Preheat oven to 375 degrees F and lightly grease doughnut pan.
In a large mixing bowl, whisk together cocoa, hot chocolate powder, flour, sugar, baking powder, baking soda, salt, cinnamon and cayenne.
Add eggs, buttermilk, vanilla, vinegar and oil and stir until combined (don’t overmix, but make sure everything is combined evenly).
Scoop into a large piping bag or freezer bag and pipe a circle around each doughnut hole.
Bake for 8-9 minutes until a toothpick comes out with moist crumbs or dry (not batter!).
Let sit in the pan a few minutes before removing to a wire rack to cool.
For the glaze, whisk the sugar, hot chocolate powder, and boiling water in a medium bowl until smooth. Add 2-3 tbsp milk and whisk until you reach desired consistency. Add additional cinnamon and cayenne to taste if desired.
Dip each doughnut into the glaze, then overturn, place on a wire rack and add sprinkles and marshmallows if desired.