Before you start, preheat the oven to 190°C/375°F/Gas Mark 5 and lightly grease and base line 2x20cm (8inch) sandwich tins.
Place all the cake ingredients into a large bowl and beat together until light and fluffy.
Divide the mixture between sandwich tins or cake cases and bake in a pre-heated oven for 20-25 minutes (10-15mins for cupcakes).
Remove from the oven and allow to cool on a wire rack.
For the icing, place the chocolate and cream in a bowl and place over a pan of simmering water for 5-10 minutes until melted, stirring occasionally. Allow to cool until thick enough to spread. (you could also use a ready made icing such as the Betty Crocker Chocolate Fudge icing).
Once cake and icing has cooled, place a layer of icing on one sponge and top with the second sponge.
Cover the cake with the remaining icing; decorate with grated/flaked chocolate and orange zest.