For the blueberry sheet cake, preheat the oven to 170 °C (convection oven). Cream the eggs, sugar and vanilla sugar – preferably in a food processor. Add yogurt, salt and oil and mix briefly.
Sift baking powder into the flour and carefully stir into the egg mixture. Line a baking tray with baking paper or grease the tray and dust with flour, spread the mixture on the tray and top with fruit.
Bake for approx. 25-30 minutes. Sprinkle with powdered sugar before serving.