This main-course soup is so satisfying that you won't notice that it has no meat except the breath of richness from pancetta. Vegetarians can cut out the pancetta and substitute water or vegetable broth for the chicken broth. Pureeing some of the beans and putting them back in the pot makes the soup feel even more substantial.
Wrap the thyme, rosemary and bay leaf in a piece of cheesecloth and secure with kitchen twine to make a sachet. Heat the olive oil and butter in a large, heavy saucepan over medium heat. Add the onion, pancetta and garlic and saute until the onion is tender, about 3 minutes. Add the broth, beans, tomatoes and herb sachet. Cover and bring to a boil over medium-high heat, then decrease the heat to medium and simmer until the vegetables are very tender, about 10 minutes. Discard the sachet.
Transfer 1 cup of the bean mixture to a blender and reserve. Add the ditalini to the soup pot, cover, and bring the liquid back to a boil. Boil gently until the pasta is tender but still firm to the bite, about 8 minutes. Puree the reserved bean mixture until smooth, then stir the puree into the boiling soup. Season with salt and freshly ground black pepper.
Ladle the soup into bowls. Sprinkle each serving with some Parmesan and drizzle with extra-virgin olive oil.