In a small saucepan over medium heat, whisk together milk, 2 teaspoons caramel sauce, sugar substitute, and vanilla extract until well blended. Heat over medium heat, stirring until steaming, about 2 minutes. Remove from heat. Transfer to a blender and process for 20 seconds until foamy. If you don’t have a blender, don’t worry about it. Just whisk the mixture continuously with a wire whisk until foamy.