Cut the tomatoes and mozzarella into thick slices.
Arrange tomatoes on a platter, alternating them with the mozzarella slices. Tuck the whole basil leaves in between the tomato and cheese slices.
Sprinkle with a generous pinch of flaky salt and several grinds of black pepper, to taste. Drizzle the olive oil and balsamic vinegar over the tomatoes, mozzarella, and basil. Serve immediately.