Microwave chocolate morsels and 1/2 cup cream in a small glass bowl at HIGH 1 1/2 minutes or until melted, stirring twice. Stir in vanilla and rum, blending well. Cool 5 minutes.
Beat remaining 2 cups cream at medium speed with an electric mixer until soft peaks form; fold cream into chocolate mixture. Pipe or spoon into a large serving bowl or dessert dishes. Garnish with additional whipped cream and grated chocolate, if desired. Chill 2 hours.