Peel the potatoes, cut and boil them in salted water. Mash the boiled potatoes and add the grated cheese. Heat oil in a pan and fry two tablespoons of flour.
Separately, mix the two egg yolks with the yoghurt and 2/3 cup (150) ml of water, and then add them to the pan with the fried flour. Stir well, wait for the sauce to come to a boil and remove from the heat. Combine it with the potatoes, add the finely diced parsley.
Beat the egg whites with a mixer into snow and also add them to the mashed potatoes. Season with salt and pepper to taste and mix again.
Bake the potato soufflé in a preheated 392°F (200 °C) oven.