Bittersweet chocolate gives this light and fluffy dessert its deep, dark chocolate color and flavor.
In a large mixing bowl, allow egg whites to stand at room temperature for 30 minutes. In the top pan of a double boiler placed over gently simmering water or in a heavy medium saucepan, heat the chocolate and 1/2 cup butter, stirring constantly, over low heat until chocolate is melted and smooth. Remove from heat; cool about 30 minutes.
Meanwhile, lightly butter the sides of 9 oven-safe 4-ounce coffee cups, pot de creme cups, custard cups or ramekins (soufflé dishes). Sprinkle the inside of each cup or dish with granulated sugar and rotate the cup until sugar has coated all of the butter. Gently shake out any excess sugar. Set aside.
Beat egg whites with an electric mixer on medium speed until soft peaks form (tip curl). Gradually add the 1/4 cup granulated sugar, beating until stiff peaks form (tips stand straight). Fold about 1 cup of the beaten egg whites into cooled chocolate mixture. Fold chocolate mixture into remaining egg whites. Evenly divide mixture into prepared cups.
Bake in a 375 degree F oven about 18 minutes or until a knife inserted near center comes out clean. Serve immediately sprinkled with powdered sugar and with raspberry sorbet, if you like. Makes 9 servings.