Cut the potatoes into small chunks and place into a saucepan. Cover with cold water, bring to a boil and cook until tender (ca. 15 mins).
Drain the potatoes and retain the cooking liquid. Return the potatoes to the pan and toss over a low heat until all the liquid has evaporated.
Measure 75ml of the potato cooking liquid and leave to stand until it is lukewarm. Put in the yeast and sugar and leave for about 10 minutes.
Mash the potatoes with the sunflower oil until smooth and glossy.
Stir the potato mash into the activated yeast and add the salt. Mix with a wooden spoon.
Gradually add the flour and stir with the wooden spoon.
Knead the dough on a work surface for a couple of minutes. Cover and leave to rest for about an hour.
Preheat the oven for 230°C.
Flatten the dough ball on the work surface and bring the ends to the middle, pinch lightly to seal and sprinkle with some flour.
Place on a lightly oiled baking tray and leave for a second proof of 30 minutes.
Bake in the hot oven for 35 minutes and leave to cool on a wire rack.