To assemble the salad, arrange the tomatoes and mozzarella on a serving plate. Drizzle with olive oil and sprinkle with salt and pepper.
Top with fresh basil leaves, basil pesto for balsamic syrup.
For the balsamic syrup, combine the balsamic vinegar and brown sugar in a small saucepan. Bring the mixture to a boil over medium high heat. Cook stirring occasionally until it has thickened and reduced by half, about 5 minutes. Set aside to cool. (This recipe makes more than needed for the salad. Leftover syrup can be stored in the refrigerator up to 1 month.)