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.