1. Combine chocolate, coffee, and Grand Marnier to a double boiler. Stir until melted and smooth. Remove from heat.
2. Separate the eggs. When chocolate has cooled, whisk in yolks.
3. In a medium bowl, whip chilled heavy cream to soft peaks.
4. In another bowl, beat egg whites until foamy and add sugar. Beat to soft peaks.
5. Fold half of whites into
chocolate until incorporated, then fold in rest of whites.
6. Finally, fold in whipped cream. Reserve some whipped cream for
topping.
7. Refrigerate for about 4 hours.
8. To serve, slice tops from oranges and scoop out flesh with a spoon without breaking skin.
9. Fill orange shells with orange mousse.
10. Garnish with
some remaining whipped cream and orange zest.