Boil 680g potatoes, peeled and cut into large pieces, until tender. Drain, mash and set aside.
Put 215ml cold water in a small pan with 85g diced butter. Bring to the boil and, once the butter has melted, remove from the heat.
Beat in 105g sifted plain flour, until the mixture leaves the sides of the pan clean, then slowly beat in 3 medium eggs. Weigh the choux pastry. Beat in the same weight of mashed potato and salt to taste.
Preheat oil in a deep-fat fryer to 160°C. Drop in small balls of potato mixture and fry until puffy and golden