Coat the bottom and sides of a 2 1/2 quart souffle dish with 2 tablespoons butter, sprinkle bottom and sides evenly with 1/2 cup sugar. Tap out excess sugar; reserve sugar for later use.
In a medium saucepan, melt the remaining 4 tablespoons butter. Stir in flour and cook, stirring occasionally, until mixture begins to bubble. Add milk, orange liqueur, melted chocolates, and salt. Cook over medium-low heat until mixture thickens, stirring occasionally. Remove from heat and allow mixture to cool for 10 minutes. Whisk in beaten egg yolks and vanilla.
In a large bowl, beat egg whites until foamy. Gradually add reserved sugar, beating until stiff. Fold whites into chocolate mixture. Gently spoon mixture into prepared souffle dish. Place souffle dish in a baking pan. Fill pan with 1-inch warm water. Bake for 55 minutes. Serve immediately with Chocolate Sauce.
Melt butter and chocolate in the microwave or in a double boiler. Add cocoa, sugar, cream, and salt. Bring to a boil. Remove from heat and add vanilla and orange liqueur.