Peel and chop the onions. Cut cucumbers into sticks. Wash, clean and slice the mushrooms. Place the Rösti corners on a baking tray lined with baking paper and bake in a preheated oven (electric range: 200 °C/ gas: level 3) for about 20 minutes.
Turn the Rösti corners halfway through the baking time. In the meantime, heat the oil in a pan, add the minced meat and fry over medium heat while turning. Add the onions and mushrooms and fry until brown.
Stir in the mustard. Season everything with salt and pepper. Add cucumbers and deglaze with wine and broth. Simmer at medium heat for about 8 minutes. In the meantime whip cream with the whisk of the hand mixer.
Stir the sauce thickener into the chopping pan and bring to the boil again. Season to taste with salt, pepper and sugar. Stir in cream. In the meantime wash parsley, dab dry and chop. Remove the hash browns from the oven.
Arrange the minced stroganoff sprinkled with parsley in a tureen. Serve with hash browns and hash browns.