Pre-heat the oven to 180°C (350°F) and grease or line a medium-sized loaf tin.
In a food processor or using a whisk, cream the butter and sugar together. Add eggs. Then add the flour, baking powder and vanilla sugar. Process or whisk for several minutes until the batter is light and fluffy (mixture will be very thick).
Pour a third of the batter into the tin and cover with half the fruit. Add another third of batter and the remaining berries. Cover with the last of the batter and smooth over until the top is fairly even.
Bake for 50-60 minutes until an inserted skewer comes out clean. Leave to cool for around 15 minutes.
For the drizzle: Heat the berries with the water and bring to the boil. Remove from the heat and mix in the icing sugar (don't be too vigorous because you want to try and keep some larger pieces of fruit rather than mash everything to a pulp). Poke holes in the cake and slather the drizzle over, piling the larger fruit up on top. Allow the drizzle to harden and then cut into slices. Enjoy