For the cake:
- 125g butter
- 240g light brown muscovado sugar
- 4 medium eggs
- 480ml cola
- 125g cocoa powder
- 250g self-raising flour
- ½tsp bicarbonate soda
For the chocolate buttercream:
- 200g icing sugar
- 100g butter
- 50g cocoa powder
- 2-3tsp water
- Cola bottles
- Red M&Ms
Preheat your oven 160°C/325°F/Gas Mark 3 and line 2x 21cm/9inch cake tins with greaseproof paper.
Measure out the coca-cola in a jug and leave on the side to stand for 5 mins so it’s not too fizzy when you add it to the mix.
In a large mixing bowl, whisk together the sugar, butter and eggs with an electric hand whisk until combined.
Gradually add in the cola and cocoa powder a bit at a time taking it in turns, one after the other, until you’ve added it all in. Whisk continuously until combined – make sure you don’t over whisk it. The mixture will be rather wet at this stage.
Next add in the flour and bicarbonate soda. Fold this into the mixture with a wooden spoon until completely combined.
Pour the mixture into the 2 cake tins, making sure you get an even amount in each. Bake in the oven for 25-30 mins until spongy to touch. You can check they’re cooked the whole way through by poking them with a knife – if it comes out clean they’re cooked, if not pop it back in the oven, checking every 5 mins until done.
Leave the cakes in the tins for about 5 mins until cooled slightly. Run a knife around the edges of the tin and turn upside down onto a wire rack, carefully flip the cakes right side up and leave to cool completely.
While the cakes cool, prepare the chocolate buttercream. In a large mixing bowl cream the butter and water with an electric hand whisk and gradually add in the icing sugar and cocoa powder. Mix until smooth and combined. If the mixture is too thick, add a few more drops of water. Leave to one side.
Decide which cake is going to be the base and which is going to be the topper. Cut the base across the top using a bread knife to make it level.
Cover the base in a generous helping of chocolate buttercream, spreading with a spatula or spoon. Pop the top cake onto the buttercream and press down firmly.
Spoon the rest of the chocolate mix into a piping bag and pipe swirls onto the cake.
Finish by topping each swirl with a red M&M, decorating the rest of the cake in cola bottles.