Preheat the oven to 175 degrees top / bottom heat. Grease a 26 springform pan and dust with flour.
Beat the eggs with butter, sugar and vanilla sugar until frothy. Mix the flour with the baking powder and the pinch of salt and mix with the whipped ingredients. Pour into the prepared springform pan, smooth it out and place the form in the oven on the lowest rail. Bake for about 20 minutes. Make a chopstick test.
Can be topped with any fruit. During the strawberry season, I mix sour cream with low-fat quark, sweeten as desired and then top with the fruit, which I then cover with cake icing.