Braise the chopped onions in 2 tbsp heated butter. Add the mince and fry until it's left in just fat.
Add the pre-boiled and finely diced potatoes. Salt and sprinkle with black pepper.
Cut the rectangular phyllo pastry sheets into 4 pieces each. Grab them in pairs, smear with the rest of the melted butter, mixed with water, put filling on and wrap up into rolls. Arrange in a tray onto baking paper.
Bake in a moderate oven until they gain a nice crisp.