For the soup: put the beetroot, carrots, parsley roots, celery and apples in a large pan and pour over 1.5 litres water, or enough to cover. Add the garlic cloves, pimento leaves and bay leaf and bring to the boil.
Simmer the soup for 20 minutes, then remove from the heat. Season with the vinegar, marjoram, salt, pepper and sugar to taste. Cool and leave overnight.
The next day, strain the soup through muslin to get a clear broth. Reheat before serving.
For the uszka filling: melt a knob of butter in a frying pan and fry the onion until softened. Strain the mushrooms, reserving the soaking liquid. Chop them finely and add to the frying pan along with the soaking liquid. Cook, stirring, until the liquid has evaporated. Season.
For the uszka dough: stir the hot water into the flour then mix in the egg. Season with salt and pepper. Knead the dough until smooth, then roll out very thin.
Cut the dough into 5cm squares. Place a small amount of the filling onto the squares of dough and fold over on the diagonal to form triangles. Seal the edges together. Wrap the triangles around your finger, sticking the 2 bottom tips together to form a ring.
Bring a large pan of salted water to the boil. Add the mushroom parcels. When they float to the top, cook for 1 more minute, stirring continuously. Drain.
Put uszka in a soup plate and then pour hot over the hot soup. Smacznego!