Beat egg yolks in mixing bowl on high speed. Until thick. About 3 minutes. Gradually beat in sugar.
In a 2-quart saucepan over medium heat, warm 1 cup of whipping cream until hot. Gradually stir half of the hot whipping cream into egg yolk mixture to temper, then stir back into hot cream in saucepan. Cook over low heat about 5 minutes, stirring constantly until mixture thickens. Do not boil. Stir in dark chocolate until melted.
Cover and refrigerate about 2 hours, stirring occasionally, just until chilled.
Chill mixing bowl for 15 minutes. Beat 1 1/2 cups whipping cream on high speed until stiff. Fold chocolate mixture into whipped cream. Pipe or spoon into cups or glasses immediately and refrigerate until serving.
Garnish with a dollop of whipping cream and shaved dark chocolate.