Combine 8 ounces of chocolate and Grand Marnier in a heavy saucepan; cook, stirring constantly, over low heat until chocolate melts. Remove from heat, and cool to lukewarm.
Beat whipping cream until foamy; gradually add powdered sugar, beating until soft peaks form. Gently fold about 1/2 cup of whipped cream into chocolate; fold in remaining whipped cream. Spoon into individual serving dishes. Chill until ready to serve. Must be kept cold.