Serves: Makes 24 pieces
1. Preheat the oven to 180°C (350°F) Gas Mark 4. Line an 18 x 28 x 4cm (7 x 11 x 1½ inch) loose bottomed rectangular cake tin with a large piece of non-stick baking paper and snip into the corners of the paper diagonally. Press into the tin so that the base and sides of the tin are lined.
2. Add the eggs, oil, sugar and lemon rind to a large mixing bowl and whisk together briefly until just mixed.
3. Mix the flour and baking powder together, add to the egg mixture with the beetroot and whisk together until smooth. Pour into the tin and spread into an even layer.
4. Arrange the blackberries over the top of the cake mixture in three rows then cook for 30-35 minutes until well risen and a skewer comes out cleanly from the centre. Leave to cool in the tin.
5. To decorate, sift the icing sugar into a bowl then gradually stir in the lemon juice to make a smooth icing that will slowly fall from a spoon. Drizzle the icing over the cake. Sprinkle with lemon rind removed with a zester or grater, then leave for 30 minutes for the icing to set.
Recipe courtesy of Seasonal Berries