Brown the sausage. Heat the olive oil in a large stockpot over medium-high heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through. If there’s excess grease, carefully drain off a bit, leaving about 1 tablespoon in the pot for flavor.

Sauté the aromatics. Add the butter and onion to the pot and sauté for 4–5 minutes, stirring occasionally, until the onion is soft and translucent. Stir in the garlic and cook for about 30 seconds, until fragrant. Add the tomato paste, crushed red pepper flakes, oregano, and salt. Cook for 1 minute, stirring constantly, to lightly caramelize the tomato paste and deepen the flavor.

Add the broth and simmer. Pour in 6 cups of the broth and add the Parmesan rind. Bring the soup to a gentle simmer.

Cook the pasta. Stir in the anelli siciliani and cook, stirring occasionally, until the pasta is al dente. Add additional broth as needed to reach your desired soup consistency.

Wilt the greens. Stir in the chopped kale and cook for 3–5 minutes, until wilted and tender.

Finish and season. Remove and discard the Parmesan rind. Add a squeeze of lemon juice to brighten things up, if you'd like. Taste and adjust seasoning as needed.

Serve. Serve warm, topped with freshly grated Parmesan and a twist of black pepper.