Leftover uncooked avocado is delicious used as a vegetable in this cake and orange juice can just as easily be sibstituted for the porter.
1. Preheat the oven to 190°C/gas mark 5. You will need a silicone Christmas tree cake mould or a deep 22cm cake tin, buttered and floured.
2. Coat the vegetables in the tablespoon of oil and sprinkle with a pinch of salt. Place the vegetables on a baking sheet and cook in the oven for 20 minutes, until tender.
3. Tip the vegetables into a food processor and blitz until chopped. Add the flour, sugar, cocoa powder and eggs and blitz again to combine. When everything is completely mixed, you may need to scrape the sides down once or twice. Add the oil and porter in a steady stream, then scrape the batter into the cake tin.
4. Bake in the oven for 45 minutes, until a skewer inserted into the centre comes out practically clean. Leave the cake to cool on a wire rack.
5. When the cake is cooled, melt the leftover chocolate in a glass bowl set over a pot of boiling water, making sure you don’t let the water touch the bottom of the bowl, then drizzle over the cooled cake.