Warm the olive oil in a large pot or Dutch oven over medium heat. Add the diced onion, chopped fennel (or celery), and carrots. Sprinkle with salt and season generously with freshly ground black pepper. Cook, stirring occasionally, until the vegetables are soft and tender, about 10 to 15 minutes.

Stir in the garlic, tomato paste, and rosemary, cooking until fragrant, about a minute. Add the diced tomatoes with their juices, cannellini beans, vegetable broth, and the Parmesan rind if you're using it. Let the soup simmer gently for 20 minutes, allowing the flavors to meld.

Next, add the pasta to the pot and continue simmering for another 10 minutes, or until the pasta reaches an al dente texture. Stir in the torn kale leaves and red pepper flakes, cooking just until the greens wilt. Taste and adjust the seasoning if needed, then serve the soup hot, with a drizzle of olive oil if desired.