In a medium mixing bowl beat sugar substitute and butter with an electric mixer on medium speed about 4 minutes or until fluffy. Stir in chocolate and vanilla. Gradually add egg product, beating on high speed and scraping sides of the bowl frequently, until light and fluffy.
In a chilled small mixing bowl beat whipping cream with an electric mixer on medium speed just until soft peaks form; fold into chocolate mixture.
Spoon into 6 dessert dishes. Cover and chill for 2 to 24 hours. Sprinkle with walnuts before serving. Makes 6 servings.