Ingredients (Serves 12)
For the frosting
Preheat the oven to 180°C, 350°F, Gas 4.
Lightly grease a 24cm/9in round, deep cake tin and line with baking parchment.
Place the carrots, stem ginger, sugar syrup and water in the large mixing bowl of a food processor and whizz until the mix has turned to a pulp. Empty the mix into a clean bowl.
Using the same food processor bowl (you don’t have to clean it), add the butter, sugar and orange zest, then whizz until pale and fluffy. Add the beaten eggs, a little at a time, and continue to mix. If the mixture curdles, simply add a little flour.
Add the flour, baking powder and cinnamon, then pulse on a low speed until well combined. Add the almonds plus 75g/3oz of the chopped walnuts and the prepared carrot pulp, and process gently until evenly combined.
Spoon the mixture into the prepared tin, level the surface and bake for about 1-11⁄4 hours, until risen and golden. To test if the cake is cooked, insert a skewer into the centre – it should come out clean. Carefully turn out from the tin and leave to cool on a wire rack.
To make the frosting, spoon the cream cheese into the cleaned processor bowl, add the icing sugar and the 3 tbsp orange juice, and whizz until smooth.
When the cake is cool, spread the frosting over the top using a palette knife. Sprinkle with the remaining chopped walnuts and cut into slices to serve.