MELT chocolate over hot, not boiling water, stirring occasionally. Beat cream cheese and sugar together until smooth. Add vanilla. Stir in melted chocolate. Sprinkle gelatin over water. Let stand 5 minutes and heat over low heat until dissolved. Fold slightly cooled gelatin mixture into whipping cream and whip until soft peaks form. Stir about 1/2 cup (125mL) whipped cream into chocolate mixture, then fold in remaining cream. Spoon mousse over crust and refrigerate until firm, about 3 hours or overnight.