Whisk the eggs and sugar together, till it is just pasty enough. Then add the oil and whisk for few more minutes.Then add the vanilla extract and whisk for few more seconds.
Sieve the flour and baking powder together, in a separate bowl. Now add the zest of the oranges into the egg batter. Now fold in the flour and orange juice too in 3 parts respectively.
Pour it into a greased tray, bake it for 30 minutes, in a preheated oven at 165-170 degree Celsius. Rest the cake.
Now to make the frosting, whisk the butter and add the icing sugar. Add the essence and cream. Whisk till the consistency is achieved.
Frost the cake with the above frosting, and using a spoon randomly spread the melted chocolate all over. Cut and serve.