Heat 3/4 cup cream in a heavy saucepan over medium heat until hot but not boiling. Remove from heat, and add chocolate, stirring until melted. Stir in peppermint extract; cool completely.
Beat remaining 3/4 cup cream until firm peaks form. Fold chocolate mixture gently into whipped cream mixture. Spoon mousse into 8 (3-ounce) cups or glasses; garnish, if desired. Chill until ready to serve.