Melt the butter, chocolate, sugars and golden syrup till smooth. Allow to cool
Preheat oven to 180 degrees. Grease and flour an 8 inch square pan well.
Beat eggs and vanilla till doubled in volume. Beat in the chocolate mixture.
Seive the dry ingredients into the wet mixture and fold in till completely moist.
Pour into prepared pan and bake for 25 minutes.
Cool in pan completely before slicing and serving.