Saute aromatics. Heat 2 tablespoons of butter in a large pot over medium heat. Add 1 cup yellow onion and sauté until softened, about 4 minutes. Add the minced garlic cloves and cook for 1-2 minutes, or until fragrant. Stir in 2 tablespoons tomato paste until combined.
Cook pasta. Slowly pour in 6 cups of chicken broth and heat to a low boil over medium to medium-high heat. Add in 8 ounces rotini pasta and cook until the noodles soften, about 9-10 minutes.
Make creamy sauce. Once the pasta is cooked, reduce the heat to low and wait 3 minutes before adding 1 ½ cups heavy cream and 1 cup grated Parmesan cheese. Stir until combined.
Add chicken. Add in 3 cups shredded rotisserie chicken, ¾ cup finely chopped sun-dried tomatoes, 2 teaspoons Italian seasoning, 1 teaspoon garlic powder, and 1 teaspoon crushed red pepper flakes. Season with salt and pepper, to taste.
Wilt spinach. Add in 2 cups fresh baby spinach and heat until the spinach has wilted.
Serve. Garnish with fresh basil or additional parmesan, if desired.
