We will start with the filling. Cook the potatoes in salty water until they soften. Leave them to cool down.

In the meanwhile peel onions and cut it into cubes. Fry onion on the frying pan with the addition of butter, until tender.

Mash potatoes with ricer. Mix them with cheese and half of the onion with some butter in a bowl. Season with salt and pepper.

Take a large mixing bowl, combine flour, 1 teaspoon salt and a bit of warm water. Knead the mixture into soft dough. Divide the dough in half.

On a floured surface, roll the dough into a thin circle (2mm thick).

Using a coffee mug cut the circles out of the dough.

Place 1 tablespoon of the filling in the center of each circle of dough and fold over. Press and seal into half-moon shapes (like shown on the picture). You can use a little warm water to seal the pierogi.

Cook the pierogi in a pot of boiling, salted water, until they float. After floating cook them for another 3 min then remove them from the water and drain.