Pre-heat the oven to 180°C (350°F) and grease or line a medium-sized loaf tin.
In stand mixer or using a whisk, cream the butter and sugar together.
Add the eggs one at a time.
Add the vanilla.
Sift the flour and baking powder together and then add to the wet ingredients.
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.