1. Put the tomatoes into a saucepan with the stock,2 tablespoons of the oil, the garlic, sugar and basil and bring gradually to the boil. Lower the heat, cover and simmer gently for 30 minutes.
2. Crumble the bread into the soup and stir over a low heat until it has thickened. Stir in the balsamic vinegar and the remaining oil and season to taste with salt and pepper. Stir a spoonful of pesto into each bowl before serving, if liked.