Place the balsamic vinegar in a small sauce pan over low heat. Reduce the vinegar to half of its volume. Set aside to cool. Lay the basil leaves across the bottom of the Bambino Rolls. Season the tomatoes lightly with salt and pepper. Layer alternating slices of tomato and mozzarella across each roll (3-4 slices of each on each sandwich). Drizzle olive oil and balsamic reduction over the sandwich. Add the roll tops and serve.