Heat up some of the oil and fry the flour. Slice the onion finely and fry it in the remaining oil.
Add the washed and cut into small cubes liver to the onions and fry it. Add the fried liver to the diluted roux and boil for 10 minutes.
Thicken with an egg and vinegar or yoghurt. Serve hot, sprinkled with finely chopped parsley.