Preheat the oven to 150C, 300F, Gas Mark 2
Place the beetroot in a food processor and blitz until smooth.
Add the margarine, flour, cocoa powder, baking powder, prune puree and caster sugar to the beetroot and blitz again
Line a square 20 cm baking tin with baking parchment and pour the mixture into it and bake for 30-35 minutes until cooked.
Allow to cool and cut into 12 pieces.
