01 - Preheat oven to 350°F. Grease a standard donut pan.
02 - In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt.
03 - In a separate bowl, whisk milk, espresso, eggs, vegetable oil, and vanilla extract until smooth.
04 - Pour wet ingredients into dry ingredients and mix until just combined; avoid overmixing.
05 - Spoon or pipe batter into each cavity of the prepared pan, filling about two-thirds full.
06 - Bake for 10 to 12 minutes or until a toothpick inserted in the center emerges clean.
07 - Allow donuts to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
08 - Whisk together powdered sugar, milk, peppermint extract, and optional cocoa powder until smooth and pourable.
09 - Dip cooled donuts into glaze, then immediately sprinkle with crushed peppermint candies and optional mini chocolate chips.
10 - Let glaze set for 10 minutes before serving.