Combine first 4 ingredients in a small mixing bowl. Set aside. Whisk together milk, egg substitute and vanilla in a medium sauce pan. Gradually add Splenda mixture, whisking until blended. Add butter. Cook over medium heat whisking constantly until mixture begins to boil; boil one minute, whisking constantly. Remove from heat. Pour filling into pie crust. Cover filling with waxed paper; chill 2 hours. Spread whipped topping over pie; garnish with chocolate shavings, if desired.