Preheat your oven to 180C (160 C for fan assisted)/Gas Mark 4. Grease two 20cm cake tins.
Mix the cake mix, oil, water and eggs gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Pour the cake mix evenly into your two greased cake tins.
Bake in the centre of the oven for 23-28 minutes or until a rounded knife inserted into the centre of the cake comes out clean, then allow to cool on a cooling rack.
Ice by sandwiching the cake together with half of the chocolate fudge icing and spread the rest around the top and sides, reserving a little for the rim of the cauldron. Put this into a piping bag with a large nozzle and pipe around the top edge of the cake. Any leftover icing you can use to make the pupils of the eyeballs.
Decorate by colouring ⅔ of the vanilla icing with green and pipe loosely over the top of the cake, using a large nozzle to form the bubbling potion. Colour the rest of the icing with orange, reserving a little to colour red. Decorate the bottom of the cake with the chocolate finger halves for logs. Pipe orange flames around the bottom of the cauldron and then add red centres to the flames. Push the jelly snakes into the top of the cake so that they give the effect that they are crawling out of the bubbling potion. Add chocolate balls as eyes and 'Hey Presto' a Halloween Cauldron to spook your friends.