Preheat the oven to 400 degrees F. Using the butter, grease 4 individual ramekins and sprinkle them with about 1 teaspoon sugar per ramekin.
In a large metal bowl, set over a pot of simmering water (not touching the bottom of the metal bowl), melt 8 ounces chocolate, stirring it with a whisk from time to time. Remove the bowl of melted chocolate from the heat.
In another bowl, beat the egg whites with 1/4 cup of the sugar until stiff and glossy.
Whisk the egg yolks into the chocolate one at a time, add 1/4 cup orange-flavored liqueur, and whisk in the remaining 2 tablespoons sugar. Fold in the egg whites and whisk until thoroughly blended.
Pour the chocolate mixture into the prepared ramekins, place on a baking sheet, and bake until they are puffed and somewhat firm, for about 20 to 25 minutes. Remove the ramekins from the oven.
While the souffles are baking, prepare the chocolate sauce, and cover to keep warm.
For the chocolate sauce: Heat the cream in a small saucepan over high heat. Add the remaining 1 1/2 teaspoons orange-flavored liqueur. Start whisking in the 3/4 ounce chopped chocolate and bring to a boil, whisking constantly. Remove the chocolate sauce from the heat. Serve immediately.
To serve: Place a ramekin on each of 4 plates and sift confectioners' sugar over the top of each souffle. Break the tops of the souffles and spoon in the warm chocolate sauce, allowing it to drip over the sides.