Sift the flour into a bowl, then pile it up and create a “well” in the centre. Put the salt into this “well”, add the baking soda previously mixed with a teaspoon of lemon juice, the sugar, the melted butter (well cooled), the eggs and extra yolk, and the grated lemon peel. Using a fork, mix everything together slowly, incorporating all the flour. When the mixture starts to become compact, continue with your hands until you have a firm but soft dough. Shape it into a smooth ball, wrap it in clingfilm and put it in the fridge to rest for 30 minutes. When the time is up, transfer the dough onto a work surface sprinkled with a little flour, and knead it again. Divide it into 4 pieces and roll the first one out using a pasta machine (or a rolling pin if you prefer), until you have a strip 2 to 3 mm thick. Do the same with the other 3 pieces. With the help of 2 teaspoons, place little mounds of Viallella along 2 of the strips, about 10 cm apart. Lay the other 2 strips on top of the ones with the Viallella, line them up and, using a pastry wheel, cut them into rectangles or squares. Put a heavy-bottomed frying pan on the stove with plenty of oil in it. When it’s nice and hot, put the “cenci” in a few at a time (they need room while they fry). Bubbles will begin to form on their surface; as soon as they become golden brown, turn them over and cook the other side. Once they are biscuit-coloured, remove them from the oil, let any excess drip off and lay them on absorbent paper. When they are lukewarm, arrange them on a serving dish and sprinkle with icing sugar.