In a large Dutch oven or soup pot, melt the butter over medium heat. Add the diced onion and cook for 5–7 minutes until softened and lightly golden.

Stir in the garlic, Italian seasoning, salt, pepper, and red pepper flakes. Cook for 1 more minute.

Pour in the chicken broth, then add the raw chicken breasts and sun-dried tomatoes (if using). Bring to a simmer, cover, and cook over medium-low heat for 15–20 minutes, or until the chicken is cooked through.

While the soup simmers, cook pasta in a separate pot until just al dente. Drain and set aside.

Remove the cooked chicken, shred it with two forks, and return it to the soup.

In a small bowl, whisk together the half-and-half and cornstarch to make a slurry. Stir it into the soup and cook for 2–3 minutes until slightly thickened.

Stir in the spinach and cooked pasta. Simmer until the spinach wilts and everything is heated through.

Ladle the soup into bowls and top with a scoop of ricotta and a sprinkle of Parmesan or mozzarella. Serve hot with crusty bread!