Brown the Sausage: Heat a large Dutch oven or heavy-bottom soup pot over medium-high heat. Add ground Italian sausage and cook for 6-8 minutes, breaking it into bite-sized crumbles with a wooden spoon, until golden browned and thoroughly cooked through. (If there is excess fat, drain leaving about 1 tablespoon in the pot for flavor).

Sauté Aromatics & Herbs: Reduce heat to medium. Add diced yellow onion to the pot with the sausage and cook for 3-4 minutes until soft and translucent. Stir in minced garlic, Italian seasoning, and red pepper flakes, cooking for 60 seconds until fragrant.

Simmer the Tomato Broth: Stir in the tomato paste, coating the sausage and aromatics for 1 minute. Pour in the crushed San Marzano tomatoes and low-sodium chicken broth, scraping up any flavorful browned bits stuck to the bottom of the Dutch oven. Bring the soup to a gentle boil, then reduce heat to low and simmer uncovered for 10 minutes to allow the rich savory flavors to meld.

Cook the Tortellini: Add the refrigerated cheese tortellini to the simmering broth. Cook for 3-4 minutes, stirring occasionally, just until the pasta turns tender and pillowy (be careful not to overcook).

Finish with Cream, Cheese & Spinach: Turn off the heat. Stir in heavy cream, freshly grated Parmigiano-Reggiano, and fresh baby spinach. Stir gently for 1-2 minutes until the spinach wilts into the hot broth and the cheese melts into a silky emulsion. Taste and adjust seasoning with kosher salt and black pepper.

Garnish & Serve: Ladle warm soup into deep bowls. Top with extra shaved parmesan, cracked black pepper, and torn fresh basil. Serve immediately with warm crusty garlic sourdough bread!