01 - Heat olive oil in a large soup pot or Dutch oven over medium heat. Add the Italian sausage with casings removed, breaking it apart with a wooden spoon. Cook for 5-6 minutes until deeply browned and cooked through. Transfer the sausage to a plate and set aside, leaving any rendered drippings in the pot.
02 - Add the diced onion, carrots, and celery to the pot. Sauté for 4-5 minutes until the vegetables are softened and the onions turn translucent. Add the minced garlic and cook for 1 additional minute until fragrant.
03 - Stir in the cubed butternut squash. Sprinkle with dried thyme, dried rosemary, salt, black pepper, and crushed red pepper flakes if using. Toss to coat evenly and cook for 2 minutes to bloom the spices.
04 - Pour in the chicken broth and bring to a rolling boil. Reduce heat to a gentle simmer, cover the pot, and cook for 15-20 minutes until the butternut squash is fork-tender.
05 - Use an immersion blender to partially puree the soup directly in the pot, leaving about half of the vegetables intact for a chunky, rustic texture. Alternatively, transfer half the soup to a standard blender, puree until smooth, and return it to the pot.
06 - Return the browned sausage to the pot and bring the soup back to a gentle simmer. Add the cheese tortellini and cook according to package directions, typically 5-7 minutes, until the pasta is tender and floats to the surface.
07 - While the soup simmers, warm the heavy cream in a small saucepan over low heat. Add the Parmesan cheese, ricotta cheese, chopped fresh sage, and a pinch of salt and pepper. Stir gently for 2-3 minutes until the cheeses melt into a smooth, fragrant sauce.
08 - Ladle the hot soup into serving bowls. Drizzle 1-2 tablespoons of the sage cheese swirl over each portion. Top with butter-fried sage leaves and a crack of freshly ground black pepper. Serve immediately while hot.