1. Peel the onions and cut them into thin rings. Clean them in water. Dry with a clean tea towel. Strain.
2. Slightly flour the liver and fry it on both sides on a frying pen with 3 spoonfuls of oil. Took away and reserve. Throw up the oil from the pen.
3. Warm up the other 4 spoonfuls of olive oil on the frying pen and add the onion. Toss it in oil over a very low flame during 10 minutes (avoid turning it golden) and add the vinegar and the wine. Cook during 5 more minutes.
4. Add the liver again, add salt and pepper, put the lid on and cook during 5 more minutes, according to the desired cooking point. Sprinkle with parsley before serving.