In a small saucepan, heat milk over low heat until warm. Add the yeast and sit for 15 minutes.

Meanwhile, put potatoes in a large pot, cover with water and bring to the boil, cooking until tender. Drain and pass through a food mill or ricer and place in a large bowl.

Add eggs, flour, sugar, oil, zest and juice and mix well to combine. Add yeast mixture and knead well, adding more flour if necessary to keep the batter from becoming too sticky. Cover and let the dough rise in a warm place for an hour, until doubled in size.

Roll out dough on lightly floured bench to approximately 2cm thickness. Use an 8cm round cutter to cut the doughnut shapes. Cut a small hole in the middle of each doughnut with a small cutter, or make a hole with your thumb. Re-roll offcuts to use up remaining dough.

Place doughnuts on a baking-paper-lined tray, cover with non-stick baking paper and a clean tea towel and let rise for another 15 minutes. Heat oil in deep fryer to 190C. Working in batches, fry the doughnuts until golden brown, about five minutes, turning over halfway through.

Remove with a slotted spoon and drain on a plate lined with paper towels.

Make the lemon icing by mixing the lemon juice with icing sugar in a shallow bowl to a runny consistency. Dip the doughnuts in icing and serve.