Heat olive oil in a large Dutch oven or heavy-bottomed soup pot over medium-high heat. Add ground Italian sausage, breaking it up with a wooden spoon into bite-sized crumbles. Cook for 6 to 8 minutes until browned and cooked through.

Add the diced yellow onion to the pot with the sausage. Sauté for 3 to 4 minutes until translucent. Stir in minced garlic, sun-dried tomatoes, tomato paste, Italian seasoning, and red pepper flakes. Cook for 1 to 2 minutes until fragrant and the tomato paste caramelizes slightly.

Pour in the chicken broth, using your spoon to scrape up all the flavorful browned bits (fond) stuck to the bottom of the pot. Bring the soup to a gentle rolling boil over medium-high heat.

Add the fresh cheese tortellini. Reduce heat to medium and cook uncovered for 3 to 5 minutes (or according to package instructions) just until the pasta floats and is tender al dente. Do not overcook to keep tortellini plump and intact.

Reduce the heat to low. Stir in the heavy cream, freshly grated Parmigiano-Reggiano, and fresh baby spinach. Simmer gently for 1 to 2 minutes until the spinach wilts into the broth and the cheese melts seamlessly into a velvety sauce.

Season to taste with kosher salt and freshly cracked black pepper. Ladle into warm shallow soup bowls, garnish with extra shaved parmesan and fresh basil, and serve immediately with warm crusty garlic bread!