Royal Caribbean's Chocolate Mousse Cake

CAKE :

• 8 oz. semi sweet chocolate 2 tbsp. orange flavor liqueur 
• 3/4 stick (6 tbsp.) unsalted (Grande Marnier) 
• butter 1 tbsp. grated orange rind 
• 8 lg. eggs, separated 3/4 tsp. salt 
• 1 c. sugar, divided 2/3 c. all purpose flour

Butter a 9 inch springform cake pan, line the bottom with waxed paper and butter the paper. Dust the pan with flour and knock out the excess. Preheat the oven to 350 degrees.
In the top of a double boiler, heat the chocolate over simmering water, stirring until just melted. Remove the pan from the heat and stir in the butter. 1 tablespoon at a time. Stir until the mixture is smooth.