Warm the olive oil in a large pot or Dutch oven, then cook the diced pancetta for about 3 to 4 minutes until browned. The pancetta should release its fat and develop browned edges without becoming hard.
Add the finely diced onion, celery, and a generous pinch of salt, then cook for about 3 to 4 minutes. Stir until the vegetables soften and pick up some golden color from the bottom of the pot.
Stir in the minced garlic and cook for about 60 seconds, then add the red pepper flakes and rosemary sprig for 30 to 60 seconds. The garlic should smell fragrant, while the rosemary releases a warm, piney aroma into the rendered fat.
Pour in the chicken stock, crushed tomatoes, cannellini beans, Parmigiano rind, 1/2 teaspoon salt, and 1/4 teaspoon black pepper, then partially cover and simmer gently for 25 minutes. Give the pot an occasional stir as the broth takes on a richer color and the beans become very tender.
Use an immersion blender to pulse the soup until about half of the beans are blended, leaving the rosemary and cheese rind intact. The broth should turn silky and opaque while still showing whole beans and small pieces of tomato.
Add the dried pasta and cook it in the soup for about 10 to 15 minutes, stirring frequently. Run the spoon gently across the Dutch oven floor as you stir so the ditalini does not settle, catch, or scorch.
Stir in the freshly grated Parmigiano Reggiano, taste, and add salt if needed before removing the rosemary sprig and Parmigiano rind. The finished soup should be thick enough to feel substantial but loose enough to settle back into the bowl.