Rinse the liver well and set in a colander to drain.
Slice the onions into thin rings.
Heat 2 T butter in skillet. Add the onions and cook until limp and translucent.
Transfer the onions to a plate and set in a warm oven.
Melt the remaining 2 T butter in same skillet. Place the thin slices of liver in skillet and salt liberally. Cook 2 minutes on med heat and then turn with a pair of tongs. Cook 2 minutes more and then place on the bed of onions.