Sift the flour, cocoa powder and bicarbonate of soda together into a large bowl. Stir in the muscovado sugar.
Blend the beetroot in a blender or food processor until smooth. With the motor running, pour in the almond milk, oil, vanilla and vinegar.
Pour the beetroot mixture on to the dry ingredients and stir until mixed. Pour into an oiled and base-lined 20 cm (8 inch) springform cake tin and bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 45–50 minutes until just firm to the touch. Leave to cool in the tin.
Meanwhile, beat the spread, icing sugar and vanilla together for the frosting in an electric mixer until soft, then gradually beat in the melted chocolate until well combined and smooth. Refrigerate for 1 hour. Release the cooled cake from the tin, spread with the chilled icing and decorate with sprinkles or rose petals.