Make the dough. Combine the flour and salt in a bowl. Add the yogurt and egg and mix until a rough dough forms. Turn out onto a lightly floured surface and knead for 2 to 3 minutes until smooth. Cover and rest for 20 minutes.

Make the filling. Boil the potatoes in salted water until tender. Drain well and mash until smooth. Stir in the cheddar and season with salt and pepper. Let cool completely.

Roll and fill. Divide the dough into two or three portions. Roll to about 3 mm thickness and cut 7.5 cm rounds. Place 2 teaspoons of filling in the centre, moisten the edge with water, fold into a half-moon and press to seal, pushing out any air.

Boil. Bring a large pot of salted water to a gentle boil. Cook the pierogi in batches for 2 to 3 minutes or until they float. Lift out with a slotted spoon and drain well.

Bacon and onions. Cook the bacon in a large frying pan until crisp; remove. Add the onion to the rendered fat and cook over medium-low heat until deeply caramelised, 8 to 12 minutes; remove.

Fry and finish. Add the butter to the pan, then fry the boiled pierogi for 3 to 4 minutes per side until golden and crisp. Return the bacon and onions to the pan and toss gently.

Serve. Top with chives and extra cheddar if desired.

Notes