TO PREPARE THE YULE LOG CAKE:
Preheat the oven to 170 °C, (165°C for a fan oven), or Gas Mark 5. Generously grease 1 swiss roll tin and line with greaseproof paper.
Mix the chocolate cake mix, eggs, oil and water in a large bowl on low speed for 1 minute until moistened. Mix on medium speed for a further 2 minutes.
Pour the mixture into your tin and spread evenly. Bake in the oven for 12-15 minutes
Whilst the cake is in the oven, lay a clean tea-towel on a work surface and dust with icing sugar.
Once baked, take the cake out of the oven and out of the tin and place onto the tea-towel, with the greaseproof paper on top.
Peel the paper off and quickly roll the cake up, starting at the short end. Wrap the towel up in the cake as you roll it. Leave to cool completely.
Meanwhile, make the chocolate frosting. Mix the butter on high speed until fully softened, then add both sachets of icing and 10ml of water. Mix on high speed until light and fluffy.
Carefully unroll your cake, it might crack don’t worry! Spread a thin layer of your icing over the cake and roll back up, use the towel to help you. Place on a plate ready for decoration.
Using the leftover icing, decorate your cake. Spread the frosting over the cake, and using a fork drag it through the icing – this will make it look more like a log.
Dust with icing sugar and it’s ready to serve.