Heat the veal stock and Madeira wine, and reduce for 20 minutes.

Meanwhile, clean and slice the mushrooms, then sauté them with the butter in a skillet.

Remove the nerves and white parts from the kidneys and cut them into pieces. Add them to the mushrooms and sauté for 5 minutes.

Add the heavy cream to the sauce and pour it over the kidneys. Let it simmer for 20 minutes.

Serve with pasta or rice.