Boil the potatoes in their skins, peel them and mash finely or run through a potato mill.
Warm a little milk and add your yeast to re-activate it and check it's alive.
Make a well shape with the flour on the table and add the potatoes. It is important to say you may need a little more of this flour ratio 2/3 00 flour 1/3 flour chestnut flour simply because some potatoes hold more moisture than others, the size of your eggs and of course the flour itself!
Add yeast, eggs, sugar, oil and lemon zest and mix well, your result should be a dough that is smooth and not sticky, add extra flour if necessary!
Knead for 5 minutes. The ladies traditionally make the dough in the morning and fry the doughnuts at sunset, if choosing this way pop your dough in the fridge to prove. If you are in a rush cover and leave outside the fridge for an hour.
Take a piece of dough and roll it into a snake as Antonia does in the photo above, twist round and join each end, in a rush use a doughnut cutter or 2 differing pastry cutters, or a glass and bottle top if you haven't got a doughnut cutter. Running short of time just fry those small snake shapes you have rolled.
Deep fry until golden on both sides. They cook quickly and will rise to the surface as they are almost ready so keep checking them.
Drain on kitchen paper and roll in sugar, best served warm!