Preheat oven to 350°F.
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 4 tablespoons butter. Stir in flour and cook, stirring occasionally, until mixture begins to bubble. Add milk, 1-1 1/2 tablespoons orange liqueur, melted chocolates (reserving 1 unmelted square of bittersweet chocolate), and 1/4 teaspoon 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 1 teaspoon 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 1/4 cup butter and bittersweet chocolate in the microwave or in a double boiler. Add cocoa,1/2 cup sugar, cream, and 1/8 teaspoon salt. Bring to a boil. Remove from heat and add 1 teaspoon vanilla and 1 - 1/2 tablespoons orange liqueur