Slice mozzarella and cut into pieces small enough to fit on tomato slices.
Add vinegar to a small saucepan and bring to a boil.
Reduce heat to low and simmer until reduced by half.
Remove from heat and allow to cool.
Cut basil leaves into strips.
Plate tomato slices.
Top each with a piece of cheese and a few basil strips.
Drizzle with balsamic reduction.
Salt and pepper to taste.
Notes
This salad tastes best when it's served as soon as possible. However, you can keep it in the fridge- either before or after serving. If making ahead, we'd recommend keeping it in the fridge for no more than 24 hours.