Preheat oven to 180 degrees C. Place butter, chocolate, sugar, water, golden syrup and vanilla into bowl and mix. Add eggs one at a time. Mix in flour and stir well. Pour into a greased tin and cook for 50 minutes to an hour until set in the centre.
Allow to cool before un-moulding.
Place butter, 100g cream, sugar and vanilla into bowl and stir well. Add remaining cream and whip together until cream holds still peaks. Either spread over cake with palette knife or serve on the side.