Heat the olive oil in a large Dutch oven or heavy-bottomed pot over medium-high heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned and cooked through, about 5-7 minutes. Drain off any excess grease, leaving about a tablespoon in the pot.

Add the diced onion to the pot and cook until softened, about 3-4 minutes. Stir in the minced garlic, Italian seasoning, and red pepper flakes (if using). Cook for another minute until fragrant.

Pour in the chicken broth and add the sun-dried tomatoes. Bring the soup to a boil, then reduce the heat to a simmer.

Stir in the chopped kale. Let it simmer for about 5 minutes, or until the kale is wilted and tender.

Add the refrigerated tortellini to the soup and cook according to package directions, usually about 3-5 minutes, or until they float to the surface and are tender.

Reduce the heat to low. Slowly stir in the heavy cream and grated Parmesan cheese. Continue to stir until the cheese is melted and the soup is heated through. Do not let the soup come back to a boil after adding the cream.

Season with salt and freshly ground black pepper to taste. Ladle the soup into bowls and serve immediately, garnished with additional grated Parmesan cheese if desired.