Heat olive oil in a large Dutch oven or heavy soup pot over medium-high heat. Add the beef sausage, breaking it apart with a wooden spoon, and cook until browned and cooked through, about 5-7 minutes. Remove sausage with a slotted spoon and set aside.

Lower heat to medium. Add the onion, carrots, and celery to the pot. Sauté for 6-8 minutes until softened, scraping up any browned bits from the sausage. Add the minced garlic and tomato paste, cooking for another 1-2 minutes until fragrant.

Pour in the beef broth and return the cooked sausage to the pot. Add the drained cannellini beans, rosemary sprig, chopped sage, red pepper flakes, and the parmesan rind (if using). Season with salt and black pepper.

Bring the soup to a boil, then reduce heat to low. Cover and simmer for 20 minutes to allow flavors to meld.

Remove the rosemary sprig and parmesan rind. For a creamier texture, remove about 1 cup of the soup (mostly beans and veggies) and blend it until smooth, then stir it back into the pot. Alternatively, use a potato masher to crush some beans directly in the pot.

Stir in the chopped kale and simmer for an additional 5 minutes, or until the greens are tender/wilted.

Taste and adjust seasoning. Serve hot, garnished with freshly grated parmesan cheese and a drizzle of high-quality olive oil.