1
Make the dough. Put the flour and salt in a large bowl, add the oil and the just-boiled water and stir with a spoon until it comes together. Knead for about 5 minutes until smooth and soft, then wrap it and leave it to rest for 30 minutes.
2
Make the filling. Grate the onion finely and mix it with the beef, the pork, the salt, the pepper and the cold water until the mixture is sticky and holds together. Keep it in the fridge until you need it.
3
Roll and cut. Cut the dough into three and keep two pieces covered. Roll one out on a floured worktop until it is thin, about 1.5 mm, and cut rounds with a 6 cm cutter or a glass.
4
Fill and shape. Put a level teaspoon of filling on each round, fold it into a half-moon and press the edges firmly to seal. Bring the two corners together and pinch them, then set the pelmeni on a floured tray under a tea towel while you do the rest.
5
Freeze any you are not cooking. Put the tray in the freezer until the pelmeni are hard, about an hour, then tip them into a bag. They cook straight from frozen.
6
Cook. Bring a large pot of salted water to a steady simmer, add the pelmeni in batches and stir once so none stick to the bottom. When they float, cook them for 3 to 4 minutes more, 5 to 7 from frozen. Cut one open: the filling should have no pink, or read 71C on a thermometer.
7
Serve. Lift them out with a slotted spoon, toss them in the melted butter and scatter the dill over the top.