Preheat the oven to 180'C.
Melt the chocolate in a heatproof bowl over simmering water (bain-marie).
Sift the flour, baking powder and cocoa powder together. In a bowl, beat the sugar and the butter together until the mixture is pale and fluffy. Beat the eggs into the butter mix one at a time. Gently incorporate the oil into the butter mix. Gently fold in the flour mix.
Divide the mix in half. Into one half gently fold in the melted chocolate. Scrape the seeds from the vanilla pod and add the seeds to the other half.
Next, fold the two mixes together to create a marble effect.
Pour the mixture into a cake tin and bake for 30 to 40 minutes.
After 30 minutes check whether the cake is cooked by inserting a skewer into the centre. If it comes out clean it is cooked. Allow the cake to cool and then transfer it to a cooling rack or plate for icing.
Place the cream and the golden syrup into a saucepan and bring to the boil. Whisk in the cocoa powder. Bring back to boil and simmer for 3 minutes. Allow the mixture to cool slightly and then pour it over the cake. Make sure the cake is cold before pouring on the icing otherwise it will melt.
«The chocolate icing should be cool before pouring over the cake but still runny. The consistency should be of a thick batter.»