Peel onions and cut them into rings. Melt butter in a pan and slowly fry onions for about 10 minutes while stirring. Then increase heat and brown slightly while stirring. Remove onions from the pan and keep warm
Heat 2 tablespoons of oil in a large frying pan. Turn 2 slices of liver in flour, tap off excess flour and fry in hot oil while turning for 6-8 minutes. Season with salt and pepper. Remove and keep warm. Process the rest of the liver in the same way
Wash the parsley, shake dry and cut the leaves into thin strips. Deglaze the frying pan with white wine and vinegar, boil briefly and put the onions back into the pan. Season with salt and pepper and arrange on plates with the liver. Serve sprinkled with parsley and crushed pink pepper