To prepare the donuts:

1. Preheat the oven to 325°F.
2. Spray two donut pans with nonstick baking spray. In a large bowl, whisk together flour, unsweetened cocoa powder, baking soda, salt, and cinnamon until combined.
3. In another large bowl, add the eggs, sugar, sour cream, vegetable oil, and vanilla extract. Whisk until the ingredients are combined.
4. Pour the wet mixture into the bowl of dry ingredients. Whisk until smooth.
5. Transfer batter to a gallon-sized ziplock bag, to form a pastry bag. Cut the bottom inch off the corner. Squeeze the batter into the donut pans filling them up halfway.
6. Bake the donuts for 10 minutes.
7. Once the donuts are done baking, let them cool for a few minutes before removing them to cool completely on a wire rack.

To prepare dark chocolate peppermint ganache:

1. Place the dark chocolate chips in a medium-size heat-proof bowl. Set aside.
2. Heat the heavy cream in a small saucepan over medium heat until it begins to gently simmer. Pour the hot cream over the dark chocolate chips.
3. Let sit for 3 minutes.
4. With a rubber spatula, slowly stir until completely combined and chocolate has melted.
5. Dip the cooled donuts into the ganache, place the donuts on a rack and sprinkle with crushed peppermints.
6. Serve and enjoy!