Cake: Preheat the oven to 180 degrees C. Prepare two 20.5cm cake tins.
Beat the eggs and sugar in a bowl with a whisk until very light and frothy. Gradually beat in the oil. Using a large metal spoon. Stir in the carrots.
Sift the flour, cocoa, baking powder, cinnamon and ginger into the bowl then stir thoroughly. Once combined add the walnuts, reserving a few for topping later.
Transfer the mixture equally between the two prepared cake tins. Bake in the oven for 25 minutes or until a knife pushed into the centre of them comes out clean. Let the cakes cool completely.
Filling and Topping: While baking make the filling and topping. Put the butter, cream cheese, vanilla, icing sugar and cocoa into a bowl and mix well. If the mixture seems very tough or dry, put it in the microwave for a few seconds. This will soften the butter and make the process much easier.
When smooth and creamy use about half the icing to sandwich the sponges and spread half on top. Scatter over the reserved walnut pieces.
We all loved it! Made it for my husband's birthday as carrot cakes are his favourite. Some slight changes as I was cooking at a beach shack and was short a few things. Used olive oil, and used self-raising flour in place of the plain flour and raising agent. Also used nutmeg and cardamon powder in place of the recommended spices. I also skipped the cocoa from the icing. - 28 Apr 2014