Mushrooms are finely chopped, add salt and sauté in fat. Cook potatoes, peel and cut into rings. Beat the egg yolks with yogurt. Egg whites are broken down into the snow and add to the egg yolks and milk. Put them mushrooms and potatoes. Gently stir and pour into a greased baking dish with butter. Bake in a hot oven until the dish is red. Serve with a green salad.