To make the filling, melt the butter in a saucepan and add the bacon, onion and carrot. Cook for about 8 minutes, until the onion is soft, but not coloured. Cool then stir into the pork or beef mince with plenty of black pepper and a little salt.
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 packed teaspoonful of filling in the middle.
Lightly wet the edges with water and pinch together tightly to seal. You can fold the edges over or crimp them with a fork if you wish.
Keep the surface dusted with flour and cover the finished dumplings with a tea towel to prevent them them drying out.
Grill the bacon rashers until crisp, then cool and crumble into shards.
Heat the remaining butter and vegetable oil in a large frying pan and brown the pierogies, in batches, on both sides. Serve sprinkled with crisp bacon shards, with sour cream, if liked.
Freezing and defrosting guidelines
Bake according to the recipe but stop before adding decoration or icing if called for. Allow to cool completely. Wrap well in clingfilm and tin foil (to prevent freezer burn) and freeze for up to 3 months.
Loosen the tin foil and clingfilm but leave to defrost in packaging at room temperature for several hours before serving. If you wish to serve the baked goods warm, place them on a baking sheet for 10 minutes in a moderate oven.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home and view the full Food safety at home video.