Tear the stale bread into roughly 3cm pieces and place on a tray. Leave aside in a warm place for around 30 minutes—this helps to dry it out.
Place the tomatoes in a bowl and season with salt and pepper. Rinse the capers, if using, and add to the bowl, along with the onion. Toss the mixture together with your hands, then stir in 2 tablespoons of vinegar and about 3 times as much extra virgin olive oil. Taste and add a little more salt, pepper, vinegar or oil, as you like.
Tear in the basil leaves, stir together and serve.
