This recipe is so easy to make. You can proportion quantities as needed for single use or larger amount that can be refrigerated.
Traditional balsamic vinegar, "Aceto Balsamico Tradizionale" is made and rigidly controlled in Italy through a complex process of reduction and aging of grapes 12 to 25 years or more. They are treasured for their soft but intense flavors and are used very sparingly.
Fortunately, there are commercial grades, Balsamic Vinegar of Modena, which tries to simulate the original. They can be mass produced, making them less expensive. They are still subject to local standards including supervision and minimum aging. Most are fine when used to make balsamic vinaigrette dressing or balsamic glaze (recipe above).
The recipe calls for either basil or tarragon. Basil goes especially well in tomato based salads. I tend to favor tarragon for all other salads.
You can also add balsamic glaze to enhance the taste of simple balsamic vinaigrette.