Knead a firm dough from the flour, water, egg and a pinch of salt. Knead it well and roll out a thin sheet. Cut circles out with a glass.
For the filling, fry the onion in a little oil and add the minced meat. Mix, allow it to fry and season it with salt and pepper. In the middle of each circle, place a little of the filling, fold the circles in 2, so as to obtain a crescent. Press the edges with your fingers to stick well.
Put the Siberian pelmeni into boiling salted water or broth. When they pop out to the surface, remove them with a slotted spoon. Serve the dumplings hot, topped with cream or mustard sauce, diluted with a little vinegar.
Optionally, you can fry them to a light tan in preheated oil.