In a mixing bowl, combine flour and oil (or melted butter) until well-blended. Add a beaten egg and enough water to form a soft dough, mixing until smooth. Cover the bowl and let it rest for 10 minutes.

Wrap the dough tightly in plastic wrap and refrigerate for at least 30 minutes.

Peel and chop the potatoes into chunks, then boil in salted water for about 15 minutes. Sauté onions until golden and caramelized.

Remove the dough from the fridge and roll it out on a floured surface to about 1/8 inch thick.

Cut the rolled dough into 4x4 inch squares, fill with potato and onion mixture and seal the edges.

Preheat your oven to 375°F (190°C). Brush the tops of the knishes with an egg wash.

Bake for 35-40 minutes until golden brown and flaky.