Trim the kidneys of any fat or skin, cut in half and remove the central sinewy bits. Heat the oil in a frying pan, add the butter and, when the butter is foaming, add the kidneys. Cook for 2-3 minutes, turn and cook for another 2-3 minutes, then remove from the pan and keep warm.
Drain off the excess fat from the pan, add the shallots and sauté for 2 minutes until soft. Pour in the wine