Take one large kidney, or two or three small kidneys, open them and remove all the fat. Cut lengthwise in thin slices, salt and pour as much boiling water as is needed to cover them. When the water is thoroughly cooled, drain it and wipe well the slices with a cloth, then put them in a frying pan with a small piece of butter. Turn them often and when they have cooked for five minutes put in a pinch of flour and season with salt and pepper. Leave them on the fire until thoroughly cooked and when you are going to take them away add another piece of butter, a sprig of chopped parsley and a little broth if needed. The kidney must not be kept too much on the fire, because in that case it hardens.