Mix together the eggs and the oils so they are well combined and pale. Mix in the dry ingredients. Slice of two ribbons for top and grate in the rest of the courgettes. Stir through all but a heaped tablespoon of the melted chocolate and the nuts if using.
Grease and line a 2 pounds cake tin and place in the the oven for 40 minutes, until you can stick a skewer in the middle and it comes out clean. Leave to cool and then pour out of tin. Drizzle over the remaining melted chocolate to decorate.