Cream fat, vanillin sugar, salt and sugar with the whisk of the hand mixer. Stir in the eggs one by one. Mix flour and baking powder and stir in alternately with milk and sour cream. Fold in blueberries.
Pour the dough into a greased, floured box form (30 cm long, 2 3/4 litre capacity) and bake in a preheated oven (electric range: 175 °C/ convection oven: 150 °C/ gas: level 2) for approx. 60 minutes (stick test). Remove the cake from the oven, let it cool down for approx. 15 minutes and turn out of the tin. Let it cool down on a cake rack. Dust with icing sugar before serving
Waiting time approx. 1 hour