Preheat the oven to 200°C.
Mix all the ingredients for the sponge or mix with a whisk in one bowl. Pour the mixture into the cake tin. Bake for about 20-25 minutes at 180°C.
Prepare the icing by heating the whipped cream to a boil, removing it from the heat and stirring in the chocolate and orange zest. Stir until everything comes together and pour over the still warm cake.