For the cake batter you will need to make a basic chocolate sponge cake.
175g butter at room temperature
3 medium eggs
175g caster sugar
175g self raising flour
50g cocoa powder
1/2 tsp vanilla essence
Pre heat the oven to 180 degrees c
Place all ingredients in a large bowl and musk together using an electric whisk.
Grease or line two square baking tins
Place mixture in tins
Bake the chocolate sponge cake for about 30-35 mins or until a cake skewer inserted in the middle comes out clean.
Place on cooling rack until cool.