1. Boil the potatoes in salted water until cooked. Drain the potatoes and cook dry for a minute or two. Allow to cool slightly, mash lightly with a fork but not too smooth – you still want to retain texture. Carefully stir in the rest of the filling ingredients and season to taste with salt and pepper. Allow to cool.
2. Preheat the oven. Working with one sheet of phyllo pastry at a time, brush it all over with butter. Spoon some of the cheese filling onto one of the short sides, but make sure you leave about 3cm open on either side. Roll the filling tightly in the pastry sheet, twist each end of the pastry like a Christmas cracker and place the roll, seam side down, on a greased baking tray. Repeat with the rest of the pastry sheets and filling.