Pre-heat the oven to 160C fan-forced and grease and flour a large, heat-proof bowl or pudding dish. Alternatively you can use several different sizes.
Place the butter and sugar in the bowl of a food processor and process until light and fluffy (you may need to scrape down the sides and repeat).
Add the eggs, one at a time, mixing between each addition and then mix in the vanilla. Add the flour and process then scrape down the sides and process again.
Remove half the batter from the food processor and add the cocoa to the processor then blitz until the cocoa is mixed in.
Alternating between the vanilla and chocolate batters, spoon the batter into the prepared tin/bowl/s. Use a skewer or knife to marble the mixture. Bake for 45 minutes to 1 hour or until a cake tester inserted in the middle of the cake comes out clean.
Leave the cake to rest in the bowl or tin for 5 minutes and then carefully turn out onto a wire rack to cool completely.
When the cake has cooled, make up the buttercream icing according to the instructions on the packet. Trim the top of the cake so that it sits flat. Place it on a serving plate.
Break off about half a packet of white Ready-to-Roll icing and knead until smooth. Flatten it out and sprinkle a tablespoon of cocoa on top. Fold the icing over and roll out again and keep repeating until all the cocoa is mixed in and the icing is brown. You may need to repeat with more cocoa to get the desired colour.
Roll out the brown icing to a large circle about 5mm thick. Check if it is big enough to cover the cake by draping it over the top.
Ice the cake with the prepared buttercream icing and place the brown icing over the top. Use your hands to smooth it out and then trim the edges. Tuck the edges underneath to make it neat.
Break off another portion of white icing and knead until smooth then roll out to about 5mm thick. Place a piece of plastic wrap over the top and cut out your desired shape to form the ‘icing’ on the pudding.
Wet the top of the cake with a little water and place the ‘icing’ on top. Prepare a small portion of green icing and roll it out to approximately 5mm thick then cut into leaf shapes. Use a skewer to make marks in the leaves for veins.
Wet the back of the leaves and place them on top of the cake. Prepare a small portion of red icing and then roll into three small even berries. Wet the berries with a little water and place them on the cake.