- With the rack in the middle position, preheat the oven to 425°F (220°C). Generously butter and flour a 12-cavity doughnut pan.
- In a bowl, whisk together the flour, baking soda and salt.
- In a large bowl, combine the oil, brown sugar, cocoa powder and food colouring with an electric mixer. Add the egg and beat until smooth. Stir in the dry ingredients alternately with the yogurt.
- Spoon the batter into a pastry bag fitted with a plain round tip. Pipe into the doughnut pan.
- Bake for 7 minutes or until a toothpick inserted into the centre of a doughnut comes out clean. Unmould by turning the doughnuts out onto a wire rack lined with parchment paper. Let cool completely.
- In a bowl, combine the icing sugar and milk. Drizzle over the doughnuts. Best enjoyed the same day.