This is like part two of my previous post as I shared my chocolate icing recipe with you, so naturally I've got to share a chocolate sponge cake recipe with for you, so that you can put that lovely icing all over it. For this again, I go back to Nigella Lawson's Buttermilk Birthday Cake recipe in "how to be a domestic goddess" but of course with a few touches added by moi. The first one of course is that mine is strictly speaking a "chocolate version" or should we say "chocolate buttermilk sandwich sponge cake", which I've done a few times for children's birthday cakes. I also add corn flour because it makes the cake kind of spongy. 
So what do you need;

200g plain flour, sifted
200g of caster sugar
25g cocoa powder
25g corn flour
1.5 teaspoons of baking powder
1.5 teaspoons of bicarbonate of soda
1.5 teaspoon of vanilla extract (not flavouring or essence)
200ml buttermilk
3 large eggs or 4 medium eggs (preferably organic) at room temperature
125g soft unsalted butter
Two 22" sandwich tins, lined with baking paper

I usually make this cake using my food processor, but you can use a food mixer or make by hand of course, just follow this process.

Before you start, line your sandwich tins with baking paper/parchment and put the oven on 180C.

First up, sift the flour, baking powder, bicarbonate of soda, corn flour and cocoa powder into a bowl and set aside.
Secondly, pour the buttermilk into a jug and stir in the vanilla extract and leave for about 5 minutes, whilst you get on with the rest of the preparation. You want the sour buttermilk to infuse with the vanilla extract.
Next, cream the butter with the sugar and then add one egg at a time as you add about 1 tablespoon of the flour mixture. Keep doing this until all the eggs are incorporated. Once this is finished, add the remaining flour mixture and slowly pour in the buttermilk mixture until everything is incorporated. 
Now, pour the mixture equally between the two sandwich tins, place into the middle part of the oven for about 20-25 minutes until a cake tester or toothpick inserted into the middle comes out cleanish – you don't want it too dry – moist cakes are king. Let the cake cool in their tins for about 10 minutes and then unmould and let the cake cool down. I usually do this in the night and then ice the cake in the morning.
Ok ! so now you are ready to ice the cake and for that see my last post. However, as this is a sandwich cake you need something in the middle. For this, take two spoons of the chocolate icing and mix it with two tablespoons of mascarpone cheese – now you have the bit that goes in the middle. Put one cake down face up, spread the mascarpone chocolate mixture on top and then place the other cake on top and spoon over your icing carefully, spreading it like butter.
This cake was a real hit with both friends and the family alike and I've already made it twice in 8 days – it's that easy.
Let me know what you think.
Recipe has been adapted from Nigella Lawson's "How to be a Domestic Goddess"