First preheat the oven (electric stove: 175 ° C / convection 150 ° C). Then wash and drain the blueberries.
Mix the butter, sugar, vanilla sugar and a pinch of salt and stir until creamy with the whisk of the mixer. Add the egg. Mix the flour and baking powder in a second bowl. Then add this to the egg-butter-sugar mixture. Finally fold in the blueberries. The dough then has a very sticky consistency.
Cut off small piles with a tablespoon and place them spaced apart on a baking sheet lined with baking paper. Lightly press the piles flat. Put the tray in the oven for 10-15 minutes. You`re done when the edges are golden brown and the center is still a little soft.
Let the cookies cool down briefly on the baking sheet and then place them on a wire rack and let cool down.