Pour balsamic vinegar and sugar into a pot and reduce by half over medium heat. Time will depend on the size of your pot (I did not use the sugar in mine).
Allow the balsamic vinegar to cool to room temp. In the mean time, plate the tomatoes, mozzarella and basil.
Drizzle olive oil and balsamic vinegar over the plate. Salt and freshly ground black pepper to taste.
Recipe Notes
If you are using a high quality balsamic vinegar then DO NOT reduce and use it as is.