Preheat the oven to 200°C (392°F) and grate the 2 onions and 1.5 kg potatoes.

Fry the bacon in a frying pan until lightly crisp, then sauté the grated onion in the rendered fat until softened.

Combine the grated potato, cooked bacon, and onion in a mixing bowl, then season with salt and black pepper.

Stir 5 tbsp sour cream into the potato mixture until evenly coated.

Lay out 2 filo pastry sheets and spread one-fifth of the potato filling over them.

Roll the filled sheets into a log and repeat with the remaining filo pastry sheets and filling.

Brush the baking tray with vegetable oil and arrange the rolled pies on the tray.

Cover the tray with aluminum foil and bake at 200°C (392°F) for 20 minutes.

Remove the foil and brush the pastry with 2 tbsp sour cream.

Bake uncovered for about 25 to 30 minutes until the pie is deeply golden brown.

Boil the 200 ml water with a little salt, then pour it evenly over the baked pie.

Turn off the oven and return the pie for 15 minutes to absorb the water.

Remove the pie from the oven and cover it with aluminum foil for 15 minutes before serving.