**Sauté Aromatics:** In a large Dutch oven or soup pot, melt butter over medium heat. Add the finely chopped onions and cook until they begin to brown, around 4-5 minutes. Stir in minced garlic, Italian seasoning, salt, black pepper, and crushed red pepper flakes; continue cooking for an additional minute until fragrant.

**Simmer Chicken and Broth:** Pour in the chicken broth, stirring to combine. Add uncooked chicken breasts and optional sun-dried tomatoes. Bring the mixture to a simmer, cover, reduce heat to medium-low, and cook for 12-15 minutes, occasionally stirring, until the chicken reaches an internal temperature of 165°F (75°C).

**Cook Pasta Separately:** While the chicken cooks, bring salted water to a boil and cook pasta to al dente according to package directions. Drain and set aside to prevent sogginess.

**Shred Chicken:** Once cooked, remove the chicken breasts from the pot and shred them into bite-sized pieces using forks.

**Prepare Cream Slurry:** Whisk together half and half (or cream) and cornstarch until smooth; this mixture will help thicken the soup when added in.

**Combine and Heat Through:** Return the shredded chicken, cooked pasta, cream slurry, and chopped spinach to the pot. Stir gently and heat over low-medium until warmed and slightly thickened, about 3-5 minutes, ensuring that spinach wilts while remaining vibrant.

**Serve:** Ladle the soup into bowls and garnish with ricotta, Parmesan, or mozzarella cheese as desired.