Preheat the oven to 350 degrees. Grease a donut pan with cooking spray. Set aside.
In a medium mixing bowl, combine flour, sugar, cocoa powder, baking powder, baking soda, salt, and espresso powder. Set aside.
In a large mixing bowl, beat eggs, milk, butter and peppermint extract.
Mix dry ingredients slowly into the wet ingredients until just incorporated.
Fill each donut cavity halfway with batter. Bake for 8 minutes.
In a small saucepan, melt chocolate wafers on low heat, mixing constantly until smooth.
After the donuts have cooled, dip each one into the chocolate and spread it evenly over the top. Sprinkle crushed peppermints on top. Refrigerate for 20 minutes until chocolate hardens.