Fudgy dark chocolate sheet cake with milk chocolate mousse frosting

Chocolate lovers, prepare to have your mind blown - this fudgy dark chocolate sheet cake is about as decadent as they come. Grated beetroot gives it a beautiful richness, whilst also adding a sneaky boost of nutrients!

By Sophie Gray
  • 35 mins preparation
  • 40 mins cooking plus cooling
  • Serves 16
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  • 225 g dark chocolate (we used 62 per cent cocoa)
  • 60 ml vegetable oil
  • 2 eggs
  • 1 cup brown sugar
  • 3/4 cup plain flour
  • 1/2 tsp baking soda
  • 1/2 tsp baking powder
  • 1/4 cup cocoa
  • 1/4 tsp salt
  • 2 tsp vanilla extract
  • 1/3 cup maple syrup
  • 1 cup ground almonds
  • 1/4 cup milk
  • 250 g (1 large) beetroot, peeled, finely grated, excess moisture squeezed out (see notes)
Mousse frosting
  • 220 g milk chocolate
  • 220 g butter, room temperature
  • 1 1/2 cups icing sugar
  • 1 tbsp golden syrup


  • 1
    Preheat oven to 180°C. Grease a Swiss roll tin (roughly 33cm x 23cm) and line base with baking paper.
  • 2
    In a heatproof bowl over simmering water, heat dark chocolate and oil until melted, stirring to mix. Set aside to cool.
  • 3
    In a bowl or processor, beat eggs and brown sugar until lightened in colour. Sift in the flour, baking soda, baking powder, cocoa and salt. Add the vanilla and maple syrup, ground almonds and melted chocolate, and pulse or mix. Add the milk then the beetroot and mix.
  • 4
    Pour into the tin and bake for 35-40 minutes or until a skewer comes out clean when inserted. Cool in tin until cool enough to handle then invert onto a rack to cool completely.
  • 5
    For the frosting, melt milk chocolate in a heatproof bowl over a pan of simmering water; leave to cool. Beat butter and sugar until pale (at least 3 minutes). Beat in golden syrup and then the cooled melted chocolate. Spread frosting onto cake with a palette knife.


We grate the beetroot in a processor then wring it out in a clean old tea towel. In hot weather a buttercream frosting like this can split or curdle. If this happens, sit the bowl in a bowl of iced water and beat it again.