Sweet & Sour Liver

I ate liver again for the second time in my life yesterday for supper. This time it was calf liver, and my father cooked it. He decided to try it in a sweet and sour sauce. This is quite possibly the easiest sweet and sour sauce ever - with only vinegar and sugar. It is amazing how something so simple could be so tasty, and it certainly goes well with the liver, and of course, onions. 

Sweet and Sour Liver
olive oil
flour
1 1/2 pounds thinly sliced calf liver
2 onions, sliced
1/2 cup white vinegar
1 Tablespoon granulated (white) sugar

Heat oil in a frying pan. Dredge the liver pieces in flour and fry for 4-5 minutes per side.
Meanwhile in a small saucepan, heat some more oil. Sauté the onion until clear. Add the vinegar and sugar and cook to reduce the mixture into a sauce. Pour sauce over liver.