Heat the oil in a heavy large pot over medium heat. Add the pancetta
and saute until crisp
and golden, about 5 minutes. Add the onion and saute until tender, about 3 minutes. Add the bread and toss to coat with the pan drippings
. Saute until the bread is crisp and golden, about 5 minutes. Add the broth, tomatoes, basil
, and crushed red pepper. Bring the soup to a boil, then reduce the heat to medium-low. Cover and simmer
until the flavors blend
, about 10 minutes. Season soup with salt and pepper.
Stir the mascarpone and sour cream in a small bowl to blend. Ladle the soup into bowls. Spoon a dollop of the mascarpone mixture atop the soup and serve.