Place a large saucepan over a low setting, and fill halfway with water. Place a second, smaller saucepan inside (creating a double boiler).
Break apart the chocolate and add to the smaller saucepan with the butter. Allow it to melt slowly – you don't want it hot.
Whip the heavy cream until stiff peaks form. You can place the bowl in the fridge until you need it later.
Beat the sugar and egg whites together until stiff peaks form.
Stir the egg yolks, orange juice, Cointreau, salt and zest together. When blended, add to the chocolate, which should be melted but about room temperature.
Carefully fold the egg yolk/chocolate mixture into the whipped cream until just blended or even still a bit streaky.
Last, fold the beaten egg whites into the mixture until just blended.
You can now pour it into individual bowls, goblets, or one large bowl. Refrigerate for at least 3 hours to set properly.
Garnish with oranges slices and chocolate curls.