If frozen blueberries are used, let them thaw on a sieve.
Preheat the oven to 180 ° C top / bottom heat.
Beat soft butter with sugar and vanilla sugar until frothy. Thoroughly stir in the eggs one by one (approx. 1 minute per egg). Mix the flour with cornstarch and baking powder and stir into the mixture alternately with the milk until a smooth dough is formed.
Pour the batter into the greased springform pan, smooth it out and distribute the blueberries on top, pressing down lightly.
Bake on the middle rack in a hot oven at 180 ° C for about 40 to 50 minutes.
Let cool on a wire rack and dust with icing sugar.