Beat the 4 egg whites with 3 tablespoons of sugar to form snow. Beat the yolks with icing sugar and vanilla sugar until frothy. Finally stir in the sour cream, egg whites and flour. Pour the mixture into a greased baking dish and bake at 170 degrees hot air or 200 degrees top and bottom heat for 30 minutes.
It goes well with cold or warm strawberry sauce. To do this, puree the strawberries and season with sugar and lemon juice.