Method

1. Heat the oven to 180°C/160°C fan/Gas Mark 4
2. Butter and line a 30 20cm traybake tin with baking parchment
3. Measure all the sponge ingredients into a mixing bowl and mix together until smooth
4. Spoon into the tin and level evenly
5. Bake for 25-30 minutes until the sponge is lightly golden
6. Carefully lift the sponge out of the tin and transfer to a wire cooling rack. Remove the baking parchment at the same time
7. To make the icing, whisk the butter in a bowl until light and fluffy. Add half the icing sugar and whisk again. Then add the remaining sugar and whisk until smooth
8. Spread the icing over the cake once it has cooled
9. To decorate, place a double row of raspberries across the centre and down the length of the cake to make a cross
10. Next place a single row diagonally from each corner to the middle. Then fill in the empty spaces with blueberries
11. To serve, cut the cake into even sized squares - it should cut into 15.