Split a pair of fresh kidneys in halves. Take out the white fat and the sinew from the centre. Cover with cold water and let heat over a moderate fire. Just before the boiling point is reached, drain from the water and cut into small pieces. Cover again with cold water and heat again, being careful that the water does not boil, or the kidneys will harden. Brown two tablespoonfuls of butter in the frying-pan, add two tablespoonfuls of flour and brown, then stir in gradually one cup of stock or water. Stir and cook several minutes, then add salt, pepper, kitchen bouquet, and one tablespoonful of mushroom catsup, and the slices of kidney. Stir until the slices are thoroughly heated, then remove from the fire. Add four tablespoonfuls of sherry, and serve with a tablespoonful of fine-chopped parsley, sprinkled over the top. If the water about the kidney boils, long cooking will be needed, to render them tender.