Preheat the oven to 160°C.
Cream the butter, icing sugar, vanilla sugar, lemon zest, lemon juice until light and smooth, then add the eggs one at a time. Combine well.
Mix the flour with the baking powder and salt, then sift this into the butter mixture. Stir gently then fold in the blueberries.
Lightly grease a medium bundt tin and dust with flour. Spoon in the batter evenly.
Bake the cake for about 50 minutes until golden and or when an inserted skewer comes out clean & dry.
Let the cake cool in the tin for 10 minutes then turn it out onto a plate.
When the cake is completely cooled, dust with icing sugar or drizzle with lemon glaze (just whisk together 2 Tbsp icing sugar with enough lemon juice to make a drizzling consistency).
Enjoy!