Step 3Sift in the flour then add the mashed potato, oil, 1tsp salt and the remaining sugar. Using your hands, mix to a rough dough in the bowl, then turn out onto a clean work surface. Roll out the dough on a lightly floured work surface into a rectangle about 30 x 25cm. Spread over the pesto in an even layer, followed by 2tbsp of the Parmesan. Step 6Starting from one long side, roll the dough up tightly into a log to enclose the filling.