Method

1. Use a vegetable peeler to pare the oranges to give several strips of zest, leaving as little of the white pith attached to the zest as possible. Bring a small saucepan of water to the boil and plunge the orange zest into it. Boil for 1 minute to remove the bitterness from the zest and make it tender, then drain and rinse in a sieve under cold running water. Set aside to drain and cool thoroughly.

2. Meanwhile, prepare a 18cm round spring-clip cake pan by greasing it with butter and lining the base with a disc of silicone paper. Preheat the oven to 190°C/Gas 5.

3. Sift the plain flour, cocoa powder, baking powder and salt into a large mixing bowl. Stir in the caster sugar and set aside.

4. When the zest is cool, cut the pieces into long, thin slivers, keeping any ragged looking bits to one side. Place the neatest slivers in a small bowl and set aside to decorate the cake after baking. Roughly chop the remainder.

5. Peel the cooked beetroot if necessary and purée the flesh using a hand blender to give a smooth, slightly textured paste. Place in a large jug or mixing bowl and beat in the eggs and vanilla. Slowly add the oil and stir until fairly smooth. Add the walnuts and roughly chopped pieces of orange rind and stir through until evenly combined.

6. Carefully add the jug of wet ingredients to the dry flour mixture, stirring only until the mixture is just combined.

7. Pour the batter into the prepared cake pan and bake in the hot oven for about 60 minutes, until a skewer inserted in the centre of the cake comes out cleanly, and the cake has shrunk a little from the side of the pan. Remove the cake from the oven and set aside to cool completely before unclipping the pan.

8. To make the frosting, sift the icing sugar and cocoa powder together. Beat the light cream cheese in a mixing bowl until soft and creamy, then slowly add the icing sugar mixture, then the vanilla extract or orange juice and beat until smooth and glossy. Pour the frosting over the cooled cake and decorate with the reserved strips of orange.