20 ounces bittersweet dark chocolate
1 1/4 cups superfine sugar
1 pound unsalted butter
2 ounces Grand Marnier
10 egg yolks — room temperature
10 egg whites — room temperature
1/4 cup superfine sugar
powdered sugar
Melt chocolate in top of double boiler over very low heat. When chocolate has melted, whisk in 1.25 cups of sugar, mixing well until sugar has dissolved. Whisk in butter and melt, stirring often. When butter is completely incorporated, remove mixture from fire and whisk in Grand Marnier.
Whip egg yolks in mixing bowl until light and fluffy. Slowly add chocolate mixture to egg yolks, whipping constantly until fully incorporated. Set aside. Whip egg whites in another mixing bowl until foamy and add remaining .25 cup sugar. Continue whipping until stiff.
Place egg whites in bowl with chocolate and fold together. When mixture is smooth and all lumps are gone, pour into buttered and floured 12-inch spring form pan. Bake at 275 for 3 hours.
Remove from oven, let rest 20 minutes. Invert onto plate and remove form. Dust with powdered sugar and serve with vanilla sauce and/or raspberry puree, if desired.