Peel the potatoes & boil until tender (around 15 mins). Strain and allow to steam dry in a colander for a few minutes. Transfer to a bowl and mash the potatoes until very finely mashed. You can put the potatoes through a ricer or fine sieve to achieve an extra fine mash if necessary. Add the butter to the potato and mash again. Sieve the flour and bicarbonate of soda into the mashed potato and stir to combine until the potato comes together as a dough. Turn the dough out onto a floured surface and knead for a few minutes until you have a soft, well-combined dough. Cut the dough into fourths. Roll each piece of dough out onto a floured surface into a circle shape, around a 1/2 inch thick. Cut the circle into quarters and fry in a non-stick pan with a little butter, for around 3 minutes on each side or until each side is browned and crispy. Repeat with each piece of dough. Serve with the sides of your choice, and some butter for spreading!