Prepare the Cocoa Glaze by combining all the ingredients and stirring until smooth. Set aside. Gradually beat the sugar into the egg using a large bowl. Beat until thick and lemony. Stir in the softened butter and the vanilla. Combine the flour, cocoa powder, baking powder, baking soda, cinnamon and salt in another bowl. Stir into the egg mixture, alternating with the buttermilk. Chill about 2 hours. The dough should still be slightly sticky. Preheat the oil in the deep fryer. Roll out the dough in batches to a thickness of 1/2" on a lightly floured board. Keep the remaining dough chilled. Cut using a floured doughnut cutter. Repeat until all the doughnuts have been cut out. Deep fry for about 2 minutes. Drain. Dip the tops of the still warm doughnuts in the Cocoa Glaze. Yields 8 Doughnuts