These Polish dumplings are the real deal and surprisingly simple to make. Serve sprinkled with crispy fried onions.
For the mushroom and sauerkraut filling, soak the dried mushrooms in 300ml/10½fl oz water and set aside to infuse for 1 hour.
Drain the sauerkraut in a colander and rinse under a tap to remove some of the acidity. Transfer to a pan of boiling water. Reduce the heat until the liquid is simmering and cook the sauerkraut for 30 minutes. Drain well.
Remove the mushrooms from the water using a slotted spoon, reserving the liquid. Finely chop the mushrooms.
Heat the butter in a frying pan over medium heat. Add the sauerkraut, mushrooms and the reserved water. Bring the mixture to the boil. Continue to boil the mixture until all of the liquid has evaporated, then remove from the heat and set aside until cool.
For the cottage cheese and potato filling, boil the potatoes in a pan of salted water until soft enough to mash (about 20 minutes). Drain well and set aside to cool.
Heat the oil in a frying pan over medium heat and fry the onions for 4-5 minutes, or until crisp and browned. Reserve a tablespoonful of the onions for the garnish.
For the dumpling dough, sift the flour into a large mixing bowl and make a well in the centre. Fill the well with the salt, oil and water. Using your fingers, gradually stir the flour into the wet ingredients, until the mixture comes together as a soft dough.
Turn the dough out onto a lightly floured work surface and knead for 5-8 minutes, or until it is smooth and glossy. Wrap the dough in a clean tea towel and set aside to rest in a cold room for at least 20 minutes.
When the potatoes have cooled, transfer them to a large bowl and crumble over the cottage cheese. Mash until smooth, then stir in the fried onions until well combined. Set aside.
To shape the pierogi, roll out the dough onto a lightly floured surface to a thickness of 3mm. Cut 10cm/4in rounds from it using a pastry cutter.
Place one teaspoonful of the cottage cheese and potato filling into half of the pastry rounds, and one teaspoonful of the mushroom and sauerkraut filling into the remaining pastry rounds. Brush a little water around the edge of each pastry round, then fold the edges together to create a bulging semi-circular dumpling, pressing the edges together to seal.
Poach the pierogi, in batches if necessary, in a deep-sided pan of boiling water for 3-4 minutes, or until they float to the surface.
To serve, pile the pierogi onto serving plates and serve the soured cream in small bowls alongside. Sprinkle with the reserved fried onions and the dill.