Place a tomato, upside down, on a cutting board.
With a sharpe, serrated blade, cut down through the tomato to about ½ inch from the cutting board. You want to cut vertical, parallel slices while keeping the base of the tomato intact so it holds together.
Gently separate the slices, being careful not to tear the slices off the tomato. Insert a slice of fresh mozzarella and a whole basil leaf between each slice of tomato.
Sparingly drizzle on a bit of olive oil and just a few drops of balsamic vinegar.
Season with salt and pepper. Garnish each tomato with a fresh basil leaf or sprig and serve.