Slice the tomatoes in half lengthwise and season with salt and pepper (tomatoes taste better when seasoned before assembly).Cut the mozzarella into pieces similar in size to the tomatoes and tear the basil leaves into manageable pieces to fit between the tomato and cheese.Quarter the prosciutto slices with a sharp knife.
Place a piece of basil on one end of each slice of prosciutto. Top each piece of basil with a piece of mozzarella and a tomato half, matching the cut sides to make a ball, then roll up in the prosciutto.
Secure each with a toothpick and set on a platter. Repeat with the remaining ingredients then finish with a generous drizzle of extra-virgin olive oil and balsamic to serve.