Kidneys in Madeira Wine

Cut the kidneys crosswise into 1/2-inch thick slices. Put the slices into flour one at a time and shake them vigorously to rid them of excess flour. Melt the butter in the pan. Put the kidneys and, stirring them frequently, cook on each side until they are lightly browned. Take the kidneys from the pan and pour Madeira into the pan. Raise the heat to high and boil briskly. Continue to boil briskly, uncovered, until the wine has cooked down to about 1/2 cup. Reduce the heat to low and, with a whisk, beat in the sour cream, a tablespoon at a time. Return the kidneys to the pan, stir to cover them thoroughly with the sauce, and simmer another couple of minutes or so to heat them through. Sprinkle with salt and pepper, taste for seasoning, and serve at once, as a first course.