Skin and halve the kidneys, removing the core. In a small frying-pan heat half the butter. Saute the kidneys for 2-3 minutes. Remove with a slotted spoon and reserve.

Cook the finely chopped onion in the remaining butter until soft and lightly browned. Add the thinly sliced mushrooms and cook, stirring continuously, until lightly coloured. Remove from the heat.

Return the kidneys to the pan. Sprinkle with the flour and blend this in carefully. Stir in the hot chicken stock and return the pan to the heat. Bring to the boil, reduce the heat and simmer for 5 minutes. Do not continue to boil as this toughens the kidneys. Add the sherry, and season with salt and freshly ground black pepper to taste.

Meanwhile, cut the slices of bread into triangles. Heat the olive oil and fry the croutons until golden brown. Remove from the oil, drain on absorbent paper and keep warm.

To serve, transfer the kidneys to a heated serving dish. Dip the edges of the croutons in parsley and arrange around the edge of the dish, sprinkle the remaining chopped parsley over the kidneys and serve immediately.