In a medium sauce pan combine blueberries, sugar, and 4 tbsp of water. Cook over medium heat until simmering and sugar has dissolved, approximately 10 minutes. Stir together cornstarch and remaining 2 tbsp of water. Stir into blueberries and heat to a full simmer. Remove from heat and stir in vanilla and blueberry balsamic vinegar. Serve warm with french toast or pancakes.
Makes approximately 1 3/4 cups of sauce. Can be made ahead and gently rewarmed before serving.