Cut the kidneys in thin, round slices. Cover them with cold water and let them stand for 1/2 hour; wash them clean, and put them in a saucepan with the water or stock, cloves, onion juice, salt and pepper. Simmer 2 hours. Put the butter in the frying pan, and when hot add the flour; stir until it is brown and smooth, and add to the kidneys. Add a little sweet herbs, and simmer 1/2 hour longer. If not seasoned enough, add a little more salt and pepper, and, if desired, 1 tablespoon of lemon juice. This dish can be prepared at any time, as it is quite as good warmed over as when it is prepared.