Combine cirnstarch, sugar, salt and milk in a blender or food processor and pulse until well blended. Alternatively, combine all ingredients in a bowl and whisk vigorously. Transfer mixture to a heat proof bowl and place over (not on) simmering water for approximately 15-20 minutes, stirring occasionally. Pudding is ready when mixture coats the back of the spoon. Add chocolate or preferred flavor and stir to combine. Add vanilla and stir to combine.