Step 1: Melt the unsalted butter in a large pot or Dutch oven over medium heat. Add the diced yellow onion and cook until softened and translucent, about 5-7 minutes.
Step 2: Add the minced garlic and Italian seasoning to the pot. Sauté for another minute until fragrant, being careful not to burn the garlic.
Step 3: Add the chicken fillets to the pot and cook, turning occasionally, until lightly browned on all sides, about 6-8 minutes. The chicken does not need to be cooked through at this point.
Step 4: Pour in the chicken broth. Bring the mixture to a gentle boil, then reduce the heat to medium-low, cover, and simmer for 15 minutes, or until the chicken is cooked through.
Step 5: Carefully remove the cooked chicken from the pot. Shred or dice the chicken into bite-sized pieces using two forks or a sharp knife. Set aside.
Step 6: Increase the heat to medium-high and add the pasta to the simmering broth. Cook according to package directions until al dente, about 8-10 minutes, stirring occasionally to prevent sticking.
Step 7: Once the pasta is cooked, reduce the heat to low. Stir in the heavy cream, milk, and grated Parmesan cheese. Stir until the cheese is fully melted and incorporated, and the soup is creamy.
Step 8: Return the shredded or diced chicken to the pot. Season the soup with salt and freshly ground black pepper to taste. Simmer for a few more minutes to heat through, but do not boil after adding cream.
Step 9: Ladle the Creamy Chicken Alfredo Soup into bowls. Garnish with additional grated Parmesan cheese and fresh chopped parsley, if desired. Serve hot and enjoy!