Method
1. Pre-heat oven - 170 °C / 340°F
2. Grease two 6-piece doughnut tins with vegetable oil or spray
3. In a large bowl, mix the flours, sugar, baking powder, baking soda, and salt until combined
4. Add in the egg, yogurt, oil, milk and grapefruit juice and zest
5. Mix, using a spatula until everything is just combined
6. Pipe the batter into each tin
7. Bake mini doughnut pans - 15 min, 170 °C / 340°F
8. Whilst the doughnuts are cooking, whisk together the grapefruit juice, zest and sugar and put to one side
9. Take the doughnuts out of the oven, leave to cool for 10 minutes in the tray
10. Dip the doughnuts into the glaze, turn over and place on a cooling rack
11. Sprinkle on the grapefruit zest and leave to cool on the cooling rack until the sugar glaze crisps up