Boil the potatoes, peel and cool.
Rinse the kidneys under running water, rub dry, cut horizontally and remove the fat strand running down the middle with a fine kitchen knife. Cut the kidneys into thin slices, season with pepper and fry in a frying pan with olive oil for 2 minutes on each side.
Then put them on a plate.
In the frying pan, sauté the shallots, add the carrot, parsley root and leek and sauté. Add rosemary, dust with flour and extinguish with wine and balsamic vinegar. Boil the liquid by half.
Thread the potatoes best on a cucumber slicer. Put lard in a frying pan, swirl the potatoes at high temperature until they take color. Then add the onion and toss until everything is browned together. Season with salt, caraway, pepper or marjoram.
If desired, strain the sauce through a sieve and season. Add the kidney slices and heat again briefly.
Serve the sour kidneys with the fried potatoes.