Peel and wash the potatoes, cut them into smaller pieces if necessary and cook them in boiling salted water for about 20 minutes. Drain cucumbers (collect cucumber water) and cut into strips (-02: in slices). Dab meat dry and cut into thin strips
Heat 2 tablespoons of oil in a coated frying pan. Sauté the meat in it in portions, season with salt and pepper. Add 2 tablespoons of oil and all the meat to the pan. Dust meat with flour, sweat it and add stock while stirring, simmer for 3-4 minutes. Peel onions and cut into thin rings. Add 2 tbsp. cucumber water, sour cream and mustard to the sauce, warm up but do not boil, season with salt and pepper. (-02: Wash parsley, shake dry. Pluck the leaves from the stalks, except for a little to garnish, and chop finely. )
Drain the potatoes and let them evaporate on the switched off hotplate. Arrange potatoes and meat on plates (-02:, sprinkle with parsley) and serve