The cleaned black liver cut into slices, which are rolled in a mixture of bread crumbs and flour and fry on both sides in very hot oil until golden color. Place in warm bowls and slices distributed on the butter. In the fat from frying put the finely chopped onion and fry until turn yellow, remove the fat and mixed with mustard, salt and pepper to taste. On slices of liver put a bit of roasted onions and a slice of lemon.