- In a bowl, combine the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
- In another bowl, combine the brown sugar and butter with an electric mixer. Add the eggs and beat for 1 minute or until smooth.
- At low speed, add the dry ingredients alternately with the buttermilk. Turn the dough onto plastic wrap and shape into a disc. Cover and refrigerate for 1 hour.
- Preheat the oil in deep fryer to 180 °C (350 °F). Line a baking sheet with parchment paper.
- On a floured work surface, roll out the dough to 1-cm (1/2-inch) thick. Cut each doughnut with a 7.5-cm (3-inch) round cookie cutter and cut the hole with 2-cm (3/4-inch) round cookie cutter.
- Fry the doughnuts four at a time, for about 2 minutes on each side and the donut holes for about 1 minute. Drain and let cool on the baking sheet.
- Just before serving, dust with icing sugar.
Reuse scraps for other doughnuts.