Heat pancetta (if using) and olive oil in a large Dutch oven or stockpot
over medium-high heat.
Cook, stirring, until pancetta has rendered fat and softened, but has not
yet browned. (If omitting pancetta, heat oil just until shimmering.)
Add onion, carrot, celery, and minced rosemary. Season with a big pinch of
salt and cook, stirring, until vegetables are softened but not browned, 10
to 15 minutes, adding more oil if pot appears dry or if vegetables are starting
to stick to the bottom.
Add garlic and cook, stirring, until fragrant, about 30 seconds. Add
tomatoes and cook, stirring, until most of their moisture has evaporated and
the mixture starts to fry. (The sound should change from a sputtering simmering
sound to a sharper crackle as vegetables start to fry).
Add Parmesan Rind and drain and rinse 2 cups of canned beans and add them to
the soup, along with 2 quarts of homemade vegetable stock, or store-bought
or homemade low-sodium chicken stock. Let simmer for 30 minutes before
proceeding to step 6.
Add pasta (unless you are planning on simmering for a long time; see step
7), zucchini, squash, and green beans and simmer until pasta and vegetables
are tender, about 10 minutes. Add spinach and cook, stirring occasionally,
until spinach is wilted, about 5 minutes. Discard Parmesan rind, if used.
Serve soup immediately as is, or continue simmering for up to 2 1/2 hours
for a heartier texture and flavor (if simmering for a long time, add the
pasta 10 to 15 minutes before serving). Alternatively, reserve half of soup on
the side, continue to simmer the other half in the pot for up to 2 1/2 hours,
and stir reserved soup back in for a soup that is hearty, but still has plenty
of bright vegetable flavor and texture. Stir in chopped herbs and season to
taste with salt and pepper before serving.