Finely chop the onions and sauté in the oil, stirring constantly, until they are a little translucent.
Now add the tomatoes and vegetable broth and simmer for a few minutes over medium heat. Then add the white beans and the Italian herbs. When the beans are hot (this takes 1-2 minutes), then season the soup with the vinegar, chilli flakes, salt and pepper.
To serve, sprinkle the soup with the grated Parmesan and the chopped basil.