stir together sugar and gelatin in small saucepan; stir in milk. let stand 2 minutes to soften gelatin. cook over medium heat, stirring constantly, until mixture begins to boil.

remove from heat. immediately add chocolate chips; stir until melted. stir in vanilla; cool to room temperature.

beat whipping cream with electric mixer on high speed in large bowl until stiff peaks form. add half of chocolate mixture and gently fold until nearly combined; add remaining chocolate mixture and fold just until blended. spoon into serving dish or individual dishes. refrigerate. garnish with sweetened whipping cream, if desired, just before serving.