Preheat the oven to 180ºC/350ºF/Gas mark 4

In a food processor, using the K-beater attachment, cream the butter & caster sugar until fluffy

In a small measuring jug, lightly beat the eggs, before adding them to the butter & sugar, a little at a time, mixing after each addition

Mix in the buttermilk and vanilla extract

In another medium-sized mixing bowl, sift all the dry ingredients together - flour, baking powder, bicarb & salt

Add the dry to the wet mixture in 3 stages, mixing after each addition

Roughly slice the bananas and mix into the batter

With a spatula, fold in the blueberries and cranberries

Pour the batter into a greased 23cm/9inch loose-based deep sandwich cake tin and make level with the spatula

Bake for 35-40 minutes or until an inserted skewer comes away clean

Leave in the tin for 5 minutes before running a sharp knife around the inside circumference of the tin and easing it away

Allow to cool on a wire rack