1. Put sugar and 1/4 cup water into top of a double boiler. Place over direct heat and stir until sugar is dissolved.
2. Set over simmering water and add chocolate. Heat until chocolate is melted. Remove from heat and set aside to cool.
3. Soften gelatin in cold water in a small saucepan. Stir over low heat until gelatin is dissolved.
4. Rinse a fancy 1 1/2 quart mold with cold water and set aside to drain.
5. Beat whipping cream, 1 cup at a time, in a chilled bowl using a chilled rotary beater, until it piles softly. Beat the confectioners' sugar and vanilla extract into the whipped cream until blended.
6. Stir dissolved gelatin into chocolate mixture and gently mix chocolate into whipped cream until thor oughly blended. Spoon into mold, and place in freezer about 3 hours, or until firm.
7. Beat 1/2 cup whipping cream, using a chilled bowl and chilled beaters, until cream stands in stiff peaks when beater is lifted.
8. Just before ready to serve, remove mousse from freezer. To unmold, loosen top edge of mold with a knife. Wet a clean towel in hot water and wring it almost dry. Place a chilled serving plate on mold and invert. Wrap towel around mold for a few seconds only. Gently remove mold. If mousse does not loosen, repeat.
9. Force whipped cream through a pastry bag and a No. 27 star tube, to decorate center and sides of mousse.