Preheat the oven to 180 degrees (convection 160 degrees). Line a baking sheet with parchment paper.
Beat the butter and sugar until frothy. Stir in eggs. Then vanilla sugar under the butter mixture
stir. Stir in the flour and baking powder. Spread the batter on the baking sheet. Spread the blueberries on the batter. Bake in the oven on the lowest rack for 25-30 minutes. Let cool, dust with icing sugar and you`re done.
Tip: Of course, you can also use raspberries, currants, etc.