1) Cook the balsamic vinegar in a small saucepan over low heat until thick, syrupy, and measuring 60ml, about 20 minutes. Set aside to cool.
2) Combine the olives, parsley, anchovies, capers, garlic, basil, pepper, and olive oil in a small bowl and toss to combine.
3) To serve, slice the tomatoes into 0.5cm thick rounds and place, slightly overlapping, on a serving plate. Spoon the olive and parsley mixture over the tomatoes.
4) Drizzle the reduced balsamic over the salad and serve.