2 oranges, finely grated zest
1 tsp baking powder
225g/8oz golden caster sugar
2 tbsp cocoa powder
100²µ/3Β½΄Η³ϊ icing sugar
pinch salt
225g/8oz self-raising flour
Β½ tsp vanilla extract
dark chocolate, grated
225g/8oz unsalted butter, softened, plus extra for greasing
175ml/6fl oz double cream
4 large free-range eggs
3 tbsp whole milk
few drops of orange juice