Beat the egg with the sugar and butter until frothy. Mix the flour with the nuts and baking powder and slowly add to the foam mixture. Pour the dough into a greased 26 cm springform pan and bake in the preheated oven to 180 ° C for about 30 minutes.
For the cast:
Beat the three egg whites very stiffly. Now stir the egg yolks with sugar until foamy, fold in the cinnamon, cornstarch and sour cream. Then fold in the berries with the egg whites (carefully, not too quickly). Now spread the topping on the pre-baked base and bake again at the same temperature for 30 minutes!