Preheat the oven to 400deg 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, melt the chocolate, stirring 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 the Grand Marnier, 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 sheets, and bake until they're puffed and somewhat firm, for about 20 to 25 minutes. Remove from the oven.
While the soufflés are baking, prepare the Chocolate Grand Marnier Sauce, and cover to keep warm.
To serve, place a ramekin on each of 4 plates and sift powdered sugar over the top of each soufflé. Break the tops of the soufflés and spoon in the warm Chocolate Grand Marnier Sauce, allowing it to drip of the sides.
Makes 4 individual soufflés