1. Pre-heat the oven to 180°C/300°F/gas 2. Mix the blueberries in a Kenwood Blender. Mix the cake flour, sugar, vanilla sugar and salt in a large bowl.
2. Mix the yoghurt, melted butter and eggs in another large bowl. Pour the mixture into the first bowl. Add the blueberries and mix until the dough becomes smooth and even.
3. Pour the dough into a tray of individual Pyrex cake tins. Cook for 20 to 25 minutes until golden brown on top.