Preheat the oven to 425 degrees. Coat a donut pan with cooking spray.
In a large bowl, whisk together the flour, sugar, cocoa powder, espresso powder, baking powder and salt.
Add the buttermilk, eggs, butter and vanilla to the flour mixture. Whisk together until just combined.
Fill each donut well ⅔ full with batter.
Bake the donuts 8 to 9 minutes or until the top springs back when touched. Allow the donuts to cool for 4 to 5 minutes before removing from the pan. While the donuts cool, make the glaze.
GLAZE
In a small saucepan, heat the heavy cream until simmering. Do not boil. Add the chocolate to the cream and stir until melted and smooth.
Dip the top of each donut in the glaze to coat and decorate with sprinkles, if desired.