Cut the kidneys in thin round slices. Cover them with cold water and let them stand half an hour; then wash them clean, and put them in a stew-pan with one quart of water or stock, a clove, two tablespoonfuls of onion juice, and salt and pepper. Simmer two hours. Put one tablespoonful of butter in the frying-pan, and when hot, add one of flour. Stir until it is brown and smooth, and add to the kidneys. Put a small bouquet of sweet herbs in the stew-pan, and simmer half an hour longer. Taste to see if seasoned enough; if not, add more salt and pepper, and, if you like, one tablespoonful of lemon juice. Take out the bouquet, and serve. This dish can be prepared any time in the day, as it is quite as good warmed over as when first prepared.