Lightly dredge the liver in flour and put aside in a bowl or on a plate.
Slice the onions thinly.
Slowly melt the butter in a frying pan. Sauté the onions very slowly, on medium heat, until caramelized.
As soon as the onions are caramelized, add the liver to the pan along with the onions. The liver should only take about 6 - 8 minutes to cook. Toss several times while cooking and add small amounts of water, in increments, if necessary. Be VERY careful not to overcook the liver!
When done, liberally sprinkle paprika over everything and mix in the vinegar to make a thick onion gravy.
Ready to serve!
* Mashed potatoes and my recipe for Hungarian Cucumber Salad are the perfect accompaniment to this dish.