Heat the oil and quickly fry the onion and potato until lightly browned. Season and set aside.
Lay out 1 sheet of filo pastry and paint with melted butter. Cut into 4 rectangles and layer, painting each surface with melted butter. Repeat with the remaining 3 sheets.
Lay a quarter of the potato mixture in the middle of each rectangle and cover with little slivers of cheese. Pull up the sides of the rectangle to make little parcels and give the pastry a twist at the top. Brush with more melted butter and cook on a baking tray for