Start with the filling. Combine the blueberries and sugar in a bowl. Lightly crush about a quarter of the berries with a fork, mix well and set aside.
To make the dough, measure the flour into a large bowl and make a well in the centre.
Crack the egg into the well with the hot water, salt and oil. Quickly beat the wet ingredients with a fork then slowly incorporate the flour, until a soft dough forms.
Knead for about 8 minutes until smooth and elastic, adding a little extra flour if it sticks. Divide the dough into thirds and keep covered.
Roll the first third out on a lightly floured surface, until it is an even 3mm thick. Using a plain, round 7cm cutter, stamp out about 12 circles. Keep the finished circles covered with a slightly damp tea towel to prevent them drying out. Repeat with the remaining two lots of dough to make about 36 circles.
To fill, cup a circle in your palm, and put a teaspoonful of berries in the middle.
Lightly wet the edges with water and pinch together tightly to seal.
Keep the surface dusted with flour and cover the finished dumplings with a tea towel to prevent them drying out.
Bring a large saucepanful of lightly salted water to the boil. Add half the pierogi and simmer for 5 minutes, stirring now and then to prevent sticking.
Drain with a slotted spoon, cover and keep warm in a low oven while you cook the remaining pierogis. Accompany each serving with a tablespoon of sour cream, and an extra sprinkling of sugar.
Freezing and defrosting guidelines
Filled, raw pierogies are ideal for freezing. In order to enjoy optimum flavour and quality, frozen items are best used within 3 months of their freezing date. Always defrost and heat thoroughly before eating. For more tips on freezing and defrosting food, read our article Love Your Freezer.