Heat the butter and oil over medium heat in a large Dutch oven or soup pot until the butter is melted and bubbly. Add the chopped onion, shallots and celery and cook for 3-4 minutes, stirring frequently, until veggies are softened. Add the garlic and Italian seasoning and cook for another 30 seconds, stirring constantly.
Remove the bay leaves then add the rotisserie chicken, rosemary, cooked rice and finely chopped spinach (if using). Cover and allow the soup to sit for 10 minutes for the flavors to meld. Taste and season with more kosher salt and black pepper, if needed. If soup is too thick, add more chicken broth. Serve and enjoy!
See Café Tips above in the post for more detailed instructions and tips.