Fruity flag traybake

100g butter,softened,plus extra for the tin
175g self-raising flour
2tbsp baking powder
50g ground almonds
4 large eggs
225g caster sugar
125g full-fat greek yogurt
zest 2 lemons
FOR THE BUTTER ICING
175g butter,softened
350g icing sugar
TO DECORATE
300g raspberries
175g blueberries

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 until smooth.Spoon into the tin level the surface.Bake for 25-30 mins until lightly golden.Carefully lift sponge out of tin,then transfer to a wire rack to cool.Remove baking parchment.To make the icing,tip the butter into a bowl and whisk until light and fluffy.Add half the icing sugar and whisk again until incorporated.Add the remaining sugar and whisk again till 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 lenth of the cake to make a cross.Next,place a single row diagonally from each corner to the middle.Now fill in empty spaces with blueberries.Cut into squares to serve.