Heat oven to 180C/160C fan/gas 4.
Butter and line a 30 x 20cm traybake tin with baking parchment. Measure all the
sponge ingredients into a mixing bowl
and mix together using an electric hand
whisk until smooth. Spoon into the tin
and level the surface.
Bake for 25-30 mins until lightly golden
and the top of the cake springs back
when pressed with your finger, and the
sides of the sponge are shrinking away
from the sides of the tin. Carefully lift
the sponge out of the tin, then transfer
to a wire rack to cool. Remove the
To make the icing, tip the butter into
a bowl and whisk using an electric hand
whisk until light and fluffy. Add half
the icing sugar and whisk again until
incorporated. Add the remaining sugar
and whisk again until smooth. Spread
the icing over the top of the cold cake.
To decorate, place a double row of
raspberries across the centre and down
the length of the cake to make a cross.
Next, place a single row diagonally from
each corner to the middle. Now fill in
the empty spaces with blueberries. Cut
into squares to serve.