This is a recipe for a yogurt soufflé cake that can be made with just four ingredients, without using flour, butter, or milk. The batter is made by mixing egg yolks, yogurt, and potato starch, and then combining it with meringue whipped until stiff peaks form, and it is finished by baking in a water bath. It is characterized by its light and fluffy texture and refreshing taste from the tang of yogurt. It is a great way to use up leftover potato starch at home and is easy enough for beginners to make. The key to making it delicious is to whip the meringue until stiff peaks form and then gently fold it in without deflating it.