For an even more intense blueberry flavor, consider using blueberry-infused balsamic vinegar. Toast the walnuts lightly in a dry pan for a nuttier flavor and enhanced crunch. If you don't have fresh berries on hand, frozen berries (thawed) can be used in the salad itself. The vinaigrette can be made ahead of time and stored in the refrigerator for up to 3 days. Be sure to whisk it again before using. Feel free to add grilled chicken or goat cheese for a more substantial salad.